Hi Alex, great idea. I've got similar plans, but in education, not housing. I can see you have asked yourself some questions that I've previously asked myself. I'll follow and hopefully will be able to give you some useful feedback.

On a side note, I have some experience building in earth (built a home with mudbricks (adobe moulds onsite) and worked in a plant that made hydraulic ram pressed bricks too), and am very familiar with the Earth Ship design. I have been scribbling earth ship designs on scraps of paper for more than 20 years :)