Looks like you have a pocket door on your WC -- excellent idea! I can't think of a way to improve this arrangement. You will have good cross ventilation even if the WC is closed up. And if you put mirrors over your vanities, that will reflect light from the opposite windows, which should be fun.

A couple of things. How many shower heads will you have? If you don't plan on 2 people taking showers at the same time, I think you could go 5' long on the shower and have that wall line up, with the toilet wall. I don't know if that is important to you. I have a 5' long shower and it is plenty long for showering. I am glad I didn't go bigger because there would have been more to wipe down.

I like the window in the toilet room, because it adds a view.

I wished there was an entry into the closet from the bathroom, so I would be able to access my clothing/dressing room following my shower. Otherwise I see you have to go into the bedroom and into the entry hall to access the closet. Not too big a deal, unless the bedroom/hall doorway is open.

No plumbing in the exterior walls. In Montana it may be against code. I don't know how thick a wall would need to be to accommodate enough insulation to allow plumbing in the walls.

Kitchen: I know this isn't part of your question, but have you posted over on the kitchen forum yet? I see 2 things from your plan that might be a problem. The first is the frig next to the cook top. There is a phrase over there that help people understand the layout of a kitchen. It goes, "ice, water, stone, fire". So this means that the ice (refrigerator) wouldn't be next to the fire (cook top). So Refrigerator (ice), sink (water), counter top for prep (stone), then the cooking area (fire), is the order for most efficiency in the kitchen. The second thing, is the pantry. I'd prefer that the pantry opened into the kitchen. But I wouldn't want it hard to access from the car either, for unloading groceries.