Actually, coming from Western Montana, (we call it the banana belt of MT), I am a little concerned by what I see.
Maybe I am not right about all of this, but I am speaking from the experience of living in a house that had 2x4 walls, (sheetrock, 3.5" of fiberglass insulation
, T-111, 12" of cellulose in the attic), and wood heat for 25 years. If you are north of Spokane, I don't think your climate is that different than the Bitterroot Valley.
The first thing that concerns me is the sink against an outside wall. Unless you are going to put a lot in insulation
in that wall, and probably forego cabinet doors, think you may have a potential problem there.
You can run your pipes through the cabinets and hang curtains on the front of the cabinets (it lets lots more heat through than cabinet doors), where the pipes are running but it is still risky to put them against the outside wall behind the cabinets. Winter may not get you this year, but what about next year?
The bathroom is going to have similar issues if you don't move a lot of warm air back there.. I don't mind a cold bedroom if I have good blankets and someone to cuddle. I slept many years in a bedroom without heat, but the bathroom is different. Stepping into or out of a shower can be pretty chilly, and a fan might make it warmer, but also will chill you quicker.
I think I would go with the bathhouse attached to the second door. It gives you more room inside and you can insulate your bathhouse and keep your pipes and shower room toasty warm. You could also move your sink to an inside wall and insulate the piping very well under the yurt. High quality heat tape will last a long time if it doesn't have to turn on very often.
I certainly am not saying this is the only way to do it, but I have spent several sub-zero nights crawling around under a house trying to thaw pipes or fixing split pipes. I plan for the worse and the rest comes easy.
Avoiding cabinets against the outside wall may also help avoid mildew where there is not good air circulation behind them in the winter.
Plan for outlets that will let you mount a ceiling fan, and several fans that will circulate warm air under the loft area to help warm the lower bedroom.
Which town will you be near? I used to drive up... I think it is 395 going from I-90 in Spokane and then north through Kettle Falls. If I remember the highway number right (last time I drove it was in the early 1980s), on into Canada and meeting the AlCan pretty far north in the middle of BC and on to Alaska.
Nice memories of driving south this time of the year and watching the northern lights dancing across BC...
My thoughts, for what they are worth. Planning now is a really good idea. Good luck to you.