I don't think it would take much at all to pull the master bedroom together and give it that cozy, finished look that you are wanting.  The basic layout of the room is exactly how I would arrange the furniture. The items that I would focus on: 1. headboard of some sort 2. window treatment 3. cohesive bedding 4. a new dresser or update the existing one with paint/new knobs.  Below are some of my ideas/inspirations for this room:

I think creating some kind of headboard is the most important element of this room to make it feel finished and give it that "homey" feel.  Because of the tall ceilings, the wall behind the bed right now just feels super empty and long.  Whether it be something upholstered or something simple with wood (like above, perhaps something your husband could put together?), having a headboard with a bit of height to anchor the room and define the bed will make such a difference.  I also love this simple neutral bedding and color scheme.

I love the simplicity and minimal look of this room too.  This is what kind of headboard I was picturing if you choose to go with an upholstered option.  I also like how simple the bedding is but it still looks chic.

I really love the idea of adding some wall sconces on each side of the bed instead of lamps.  I think this will make the most of the space and make it feel roomier (while also adding some interest to that big wall).  I love this size of bedside table too, the rug, layered bedding, and tall mirror (adding a leaning mirror like this, even if layered behind the bedside table will open up the room).

A bit more modern, but I love the mix of the distressed furniture with the more graphic pieces and the cozy layered neutral bedding.

One other idea to break up the space and make it feel larger, would be to do an accent wall behind the bed in a slightly darker color (doesn't have to be as dark as this, could even be a navy or gray tone).  I love this overall bed setup with the bedside tables, bedding, and sconces.

More bedside sconces and simple, neutral bedding.

Love this mirror above the bedside table to help enlarge the space (you could even do matching mirrors on each side of the bed too).  I also like all these blue tones if you wanted something other than white/neutral bedding.

Another neutral space with lots of pattern and midcentury lines.  I think the sleeker look will work perfectly in this room to maximize the space and make it feel larger.  Love the simple bamboo shade on the window and the simple headboard too.

Really love the mix of traditional, rustic, and modern in this room.  The antique headboard is a little more modern with the color/paint finish and the all-white bedding opens up the room.

Another simple bamboo shade for the window- I think this type of window treatment would be perfect for this room.  I also love the bedside tables, jute rug, bedding, and sconces beside the bed.

Another sleek, modern space- I love how all the white opens up this room and the patterned rug is beautiful.  If you wanted to do a modern mirror like this above the bed instead of a headboard, I think that could also give the bed that finished look.

Old windows/doors are just another idea for adding height behind the bed.  I really love this mix of charcoal grays, browns, and white bedding too.  Floor lamps like this on each side of the bed would also be a great option that would add height and anchor the space.

I saw this idea and thought of your closets- I like the mirror on the sliding door because it would open up the room so much.  Not sure if we could manage to do one door that slides all the way across, but just something to think about.

Beautiful blend of modern + antique pieces in this bright traditional bedroom.

Love this navy color on the wall, the beautiful bedding, neutral curtains + bamboo shade.

Another example of tall mirrors on each side of the bed to open up the room.  I also love the simple fabric roman shade for the window.

Another idea for bedside tables that I thought was neat, looks cool but also saves a lot of space- and possibly something your husband could make too!

Below are my initial floor plan thoughts for this space. I'd love to really make the fireplace area a focal piece of the room.  I love the tile that you have picked out for modernizing it and I think all it's missing is a statement piece above it (some kind of artwork/mirror/gallery wall/shelving).  I even thought about using that giant gold mirror from the guest bedroom possibly over it (and that would really open up the whole room too and make it feel bigger).  Other than that I would love to try the draft table floating away from the wall and facing the entrance of the room.  Then I think we would have space for a floating conversation area facing the draft table (maybe 2 chairs and a small table?).  I'd also love to add either open wall shelving or bookcases on each side of the window behind the draft table. 

Below are some inspiration photos to help you visualize some of my ideas and parts of the floor plan above:

I love the simplicity but rustic, modern flair of this room.  I like the idea of having your work table away from the wall and facing the entrance of the room too with a rug below.  A nice console table or bookshelves on the wall behind it would add some dimension and fill the walls better.    

Another simple, rustic space- I like how they highlighted the work table with the industrial pendants above it.  I'd like to add some kind of lighting, either wall mounted or from the ceiling over your work table to really anchor the space.  

I like all the old signage and pictures and it reminded me of some of your pieces that you have.  It would be neat to find some old metal cubbies/organizers like they have to hang on the walls for extra storage, but they also fit in with the overall decor.  I also noticed how they used an old chest on the left hand side for a printer stand- perhaps we could utilize your old chest in here for something similar near you desk.

Love this mounted wall light above the drafting desk and the overall simplicity of this space.

I'd love to add some floor lamps or table lamps too for some ambiance and I like these industrial style lamps.  I also like how they have the desk floating in the center of the room with a little seating area facing it- this is one of the options I was picturing for your space, but leaving a walkway behind the seating area so you can easily pass through since this is an entry space.  Love the old maps for wall art too- we could easily duplicate something like this with old maps, architectural drawings, or something similar and then frame them in more modern frames.

Loved this eclectic mix of wall art and the combination of old and new in here.  I think one or two leather club chairs like this might fit the space better than a loveseat or settee and it would give us room to add a small side table/table lamp to make the sitting area feel cozy and complete.  

This is a slightly smaller draft table than you have but I do like it at an angle in a corner too.  This is just something we could try that might open up a lot more space.

I like this overall style of decor and the accessories for this room- would love to incorporate some leather chairs and a cowhide rug.

Super simple but functional- love the antique pieces and the simple sheer curtains.

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Another small space with a floating desk in the center.  I'd love to add some other furniture pieces like this metal filing cabinet, shelving, etc. to fill the walls.  One or two pieces with some height will also help anchor the room.

I love this industrial shelving- I'd like to do some kind of shelving in the room on each side of the window (the window your drafting table is under now)- whether it be free standing bookshelves or something attached to the wall like above.

I also really love the neutral color scheme of this space (especially those curtains).  I think some light linen fabrics like this would be so pretty with the wall/trim color you have now.  I also really like the industrial shelving and console table they have added.

Another space with a floating desk- love the open shelving, jute rug (great for dogs!), and the elcectic mix of accessories.

Another drafting table angled in a corner, but I especially love the other furniture pieces they have in here and how they anchor the room and fill the space while giving you SO much extra storage!  I've listed a few similar options at the end of this section, but these are also things I can find while out thrifting too.

Love this lighting over this workspace and the map/chalkboard wall art.  We could easily fill the walls with some items like this (chalkboards, bulletin boards, calendars, etc.) that would be usable in an office space but still look good as wall decor.  

A super simple space with vintage filing cabinet, industrial lighting, and overall minimal feel.

This is one of my all-time favorite office spaces- I love the mix of old + new and the cozy feel.  These bamboo shades add so much warmth and texture to a room and they look great even without curtains on top.  I have these on all my windows and they are very inexpensive too.  

Love these ledges as a wall art/storage option too.

I really love this layout with the bookcases behind a work table (especially with those wall sconces in between).

One more idea for the curtains- these are just made from canvas dropcloth- an inexpensive but super  simple look for windows that would fit perfectly with your rustic modern style.

You can click each item to see price + more details.  If the item doesn't have a link, it is from one of my showroom catalogs so I've listed the price below it!  These are just some ideas to get us started and we can of course look for similar items in different prices ranges/styles/etc.

Your living room doesn't really need much to pull everything together nicely.  I know you mentioned getting a new couch and I added some leather options at the end of this section, but either way I think we can make the existing couch work if needed with some new pillows and accessories.  See my favorite inspirations for this space below:

I love the overall rustic, neutral feel of this space just as far as inspiration for wall decor and accessories for you room.  Love the simple rug, pops of green, leather, and woven elements.  I'd love to do some kind of clustered gallery wall like this possibly over your couch, here they used botanical prints which I love, but we could also do something equestrian too.

I also love this neutral space with pops of navy and blue.  Would love to add a coffee table like this to your room if you are open to replacing the ottoman (I've listed some options below).

I love how they used the stacked books beside the couch for a perfect space-saving side table.  I also like the picture ledges with photos as another idea for behind your couch.

Loved this overall style for your living room with the leather, navys, and modern rustic style.

A gorgeous leather couch with lots of navy and printed pillows- love the black and white print above the couch too.

I really love the built-in bookshelves you have in this room and the colors you have painted them.  I think we have room to mix in just a few more accessories for some pops of color + add layers of objects (see above and below) 

This space reminded me a lot of yours, I love the burlap-look ottoman, shelf styling, and the pretty curtains.  I'd love to add some neutral curtains with a little texture that drape to the floor similar to these and maybe mount them above the window frame too.

Love this coffee table (this is an antique/vintage piece which is something I could find pretty inexpensively for you if you'd rather have that than something new!) and I also love the addition of a floor lamp by the couch- this might be perfect for making the couch area feel finished without taking up a lot of space. 

Love all the grays and neutrals and this industrial-chic coffee table!

I really like the contrast between the more traditional leather couch here and the more modern side table- would love to mix some modern side tables in with your couch possibly if we could fit one or two.

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Another gorgeous leather couch, tufted ottoman, and I really also love this curtain set-up- bamboo shades + neutral, flowy linen panels.

I think if you wanted, you definitely have room for a slightly larger, longer console table on the right hand wall of the room (the wall opposite the window).  I was picturing a set-up similar to above with lots of accessories and baskets/trunks underneath for extra storage.  I also love this idea of the picture ledges filled with lots of old mirrors for some wall art (maybe above the couch- would really open up the room?)

One more modern-chic space with a leather couch, navy tones, and lots of neutrals- love the overall styling here.

A more eclectic gallery wall for above the couch and some clean-lined midcentury side tables are also an option for accessorizing the couch area.

My first priority in the guest bedroom would be to hang a curtain on the window behind the bed (extra high and wider than the window- see below).  This will anchor the bed area and open up that little nook and make it feel bigger.  I'd probably also get a taller lamp for the bedside table and put maybe a floor lamp or something on the other side to balance it out.

Love the curtains in this room and how they are hung behind the bed.  I also liked the mix of modern with traditional furniture which reminded me of your space.  

Another example of curtains hung behind the bed with a matching bamboo shade.  I'd also love to layer the bedding up a little more to make it feel extra full and cozy for your guests- adding just a few more pillow shams and maybe a quilt or throw.

Loved this mix of antique and modern elements for this bedroom set-up.

More simple and modern style with the bed still in front of the window- love the leaning mirror to open up the small space.

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I also loved this wall art arrangement and it reminded me of the unique angles/nooks in this bedroom. I know you had lots of pictures/frames piled up in here so maybe we could cluster them and hang them similar to this to fill some of the walls in here.

Love this old iron bed and all the white bedding with the simple jute rug.  

Simple white curtains behind the bed and a few more pops of color throughout the wall art and bedding.

Another antique iron bed and a mix of antique and modern details- love the patterns and colors in here. 

I love how cozy and udone this bedding feels and also think some wall sconces like this would be perfect for your bed nook in here and save some space.