Get a magnetic vent cover on amazon (google it) and close the floor register, they can easily be cut and shaped. Also if you use a regular floor register, take the wall register off, put the floor register in, and put the wall register on top of it... It looks like there is enough space under the wall register, if not trim some of the wood to raise it up. If you not handy enough, call a local handyman they will fit everything in 10 min. Good luck

I don't think you can go wrong with narrow builtins around the fireplace, under the windows. The space can't really be used in another way, and having storage is always a plus. Think carefully about whether you want closed or open storage, or a combination. I also think the soft green you had on your accent wall would look great in your new dining space. Greens always look good with wood. If the dining area has a lot of windows, you could use a deeper color. I'd keep the rest of the main spaces one neutral color. You can use the third option from your builder for a different bedroom color, which I think is always nice. I'd make a floorpan with actual dimensions, and measure all your large current furniture pieces. That will help you see whether or not they can fit in the spaces, or if you should sell them prior to the move. I wouldn't buy anything until after you're in. If your hutch can't fit in the dining area, you may be able to use it on the far side of your living space, across from the fireplace, in an entry, or another room.

I would stain the wood beam and corbels a dark brown. Here are some Benjamin Moore colors I think would be nice. I found that the darker colors seemed to look better than some of the lighter ones I originally picked. With any one of these, there is an opportunity to add more color in the soffit and gable ends. I sampled Storm Cloud Gray on the garage.

What is your long-term plan for the space? Do you ever foresee being able to do a full remodel? Is this all stuff you are going to DIY or are you hiring out? Is there a serious budget constraint or just the hassle of being without a bathroom? Since you are going through the effort of installing a new tub, framing a new alcove and will need to waterproof and finish your walls, why don't you do just that. Use classic white tiles - either 4x4 or subway, no accent tiles. Let the tub and alcove be a white fixture in the space just like your toilet/vanity. The epoxy paint solution gets varied results. It depends on the skill of the painter and how he preps the tiles, and how hard you are on them. I know they say bathtubs will last a couple of years (maybe 8-10 if you are especially lucky). I would think wall tile would have a decent lifespan because it's not exposed to much friction. If that's not a solution, at a later date you can either finish out the rest of the room in matching tile or beadboard wainscotting. As for the floor, those are 'through body porcelain' and they are pretty darned durable. We have them in our bathroom and they are set in about 6" of concrete. I would work on those stains a bit more. We were pretty aggressive in sanding them as ours had a layer of tile over them. You can always address the floor later too, as long as you 'do no harm' right now. Don't glue anything down on it that you would want to remove later. I'm going to echo the 'no' to the LVP that looks like encaustic tiles, it may seem trendy now but will be sorely dated in the future. We had similar challenges renovating our main floor bathroom with little kids. Mine took sponge/laundry tub baths and we showered at the neighbors' in the most critical phases. And I think we installed the toilet about 3 different times over a 9 month period.