In your Edelweiss house you use 2x6 studs. Why not use 2x4 studs and add 2" rigid on the inside?
...2x4s can be used for homes no problem, but it definitely fattens up the posts required between windows. The sections of wall between the south-facing windows in the Edelweiss house are fully filled with 2x6s, and would have been much thicker if the structure were made out of 2x4s. Designs with higher levels of glazings...