Yes, in an ideal situation (especially for a residence) heat transfer down below needs to be taken seriously as there is a lot of bridging from the building materials. The same is true for moisture transfer. Since the 2" rigid foam can support a lot of weight, placing it on top of your subfloor and taping prior to installing a floating Advantec working floor will place a break in mechanical bridging which makes for a lot more comfort...even though the actual insulation value is only R-10 or so.
Making wall panels that can hinge open in nice weather is a very nice way to go. You get full wall value insulation in the very cold months and can open up when it's really pleasant.
If you can't or don't want to do gutters, just be sure you are careful in how you design your roof overhangs so that precipitation heads well away from the structure and water doesn't "wrap around" the bottom edge which can cause significant moisture damage, even in a short time period. Were I doing what you are doing, I'd go with a relatively steep roof pitch and use metal roofing so snow slides off easily, too.
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The most expensive tool is the one you buy "cheaply" and often...