House design. Practical suggestions based on experience.?

I'd suggest looking at AAC autoclaved aerated concrete for a building material. It's green, energy efficient, versatile. I've been through a few houses under construction with AAC and spoke with a builder and an architect (was one of those home tour deals). There appears to be no real downside to the material. Not cheap, but energy costs will continue to skyrocket. It's flexible. It's bug resistant, mold resistant, termite resistant, and offers sound and thermal insualtion.

I'd suggest concrete floors as well. Lots less trouble than other flooring types and "changeable" if you want to in the future with no fuss involved. Again, been in houses with concrete floors. Was a local architect/builder who put it in his home years ago and was still thrilled with it. Looked good. Incredibly practical and cost efficient.

Would encourage you to consider a metal roof from discussions with a different architect. Though you have to figure out how to deal with potential noise during storms.

Many countertop choices--possibly concrete is the answer again.

That's a lot of information you're requesting. Obviously you're going to do well to interview many different architects before going forward.

From what I've seen if you go with geothermal you're pretty much covered and don't need solar.

Tankless water heaters can be a little picky, not playing well with the anti-scald valves in all the new tub/shower fixtures sold these days. You pretty much have to run the fixture at maximum water flow (no water saving shower heads for instance) to keep the water heater engaged. Otherwise you take cold showers. You might to better with a hydronic system hooked up to the geothermal.

Kitchen counters that are literally rock hard result in a lot of broken dishes and glass wear. Have you considered reclaimed wood with a poured epoxy surface? It's softer and beautiful.

It's possible to get strong types of glass that would be very secure. Look to sources for things like commercial buildings.

The style of home that came to mind considering the two masters is something common on the east coast from the early 1800's where the front door is centered with the main rooms entered first and the large kitchen just beyond, with two equal wings to either side that contain the bedrooms etc. I should think that layout would work. I'd put the laundry room behind the kitchen (off the back.) I prefer to have all the appliances lined up along one wall rather than on two sides of the room. I find it easier to access everything and it allows for room to spread out if necessary.

That's not all your issues but it's what I have some experience in.

Have fun.

Are we talking about extending the house itself, adding additional rooms, decks? If you are just renovating the interior of the house, the normal steps are to call three contractors in, get prices and then pick out which one is the cheapest. Most contractors will have knowledge on the architect end and come up with designs. After they come up with a design, then work begins. Usually, removal of walls, plumbing, electrical, putting drywall up again, relocating electrical, plumbing, painting, flooring, base molding, crown molding, and then furniture. If you adding an addition, first an architect or contractor needs to draw up the plans, and then present it to the town hall for property lines and to see if these additions are allowed. :-)