I would like comments for changes before I proceed to builder. The house will be in a northern climate so snow and ice are considerations. Also plan to retire there. Image link:

I live in upsate NY, so the weather is humid continental and heat is up to average 28 celsius in the summer and average low to 14 in the winter - similar to your temp except for yours is less humid. I get the morning sun in the kitchen, which is hot and strong in the summer. I don't cook at all, so I don't get any of that hot morning sun where I want it in the living room (I spend the most time in the living room and I love the heat). I get the afternoon sun in the living room, which is very weak and doesn't do me any good. Even on a sunny day in the middle of summer, I have to put the lights on in the living room because the afternoon sun is so weak. It doesn't help that there are lots of tall trees back there as well (blocking the sun even further). If I ever buy another home, I'm going to be sure the morning sun comes into the living room. I can't stand the cold winters, so I hibernate! I keep everything closed up with super insulated curtains on all the windows. I don't open them up until the Spring. So you will have to consider all these issues (when the sun comes into your home, where you want the strongest sun, and where you want the weakest sun) when building your home. That will also affect your heat. It's so hot in our summers that I have the a/c on and close up the curtains on the hottest days (and open up the windows at night). Another thing you'll have to consider is if you want to grow a vegetable garden, where is the best location for that on your property. I have a friend who is an excellent gardener. She needs to think about the location of her garden to be sure she gets the correct type of sun - when and where. Best wishes and congrats!

Family room would make a good dining room, but guests would have to walk through the bedroom area and past the bathroom (or through the kitchen) to get to it from the living room. Do you entertain dinner guests often? Consider using a banquette on the wall of the dining area with a long trestle table and some chairs.

I think you've done about the best you can do. When a room is really busy with odd angles, you have to go a bit simpler with the decor and eliminate clutter. I think your mock up looks a lot better than reality because the clutter is gone. For starters, the front door opens the wrong way into the room, IMO. Can you reverse that so you're opening up to a welcoming place to sit and not the TV screen? If you need more seating for entertaining, consider a round hassock for your coffee table so it can double as seating. Use a tray on it and keep it about the size of your table now. The room can't handle a larger one. Place a chair left of the fireplace. Add a large colorful piece of art 5" above the mantel. It can be as wide as the firebox opening. To tackle the wall over the sofa, I would use the pieces you have already to make a gallery that actually just incorporates the window that's there with the stained glass. Center the sofa on that entire wall and then plan your gallery to work above it just like the window does (at the same height and with a similar volume.) Eliminate the shelves. Maybe use them right of the window in the adjoining room, or the kitchen.