I agree, with a house like yours space is an issue, unless you put the bales on the outside. I've done that with brick or concrete, put foam on the outside. Straw would work too. With the mass on the inside you get a much more stable environment, the walls warm or cool the room quickly once you close the door. With a corrugated skin you have no mass, but I'm sure you found speed and cost to be reasonable compensation.

Window treatments are pretty much the same as with stick built homes except that the sill is much deeper. I've heard no more complaints about windows in 2' walls than in 6" walls.

Our walls didn't leak. 2" of sand/clay/lime render took care of that. The sand and clay came from a pit the owner dug on the property.