Spent some time talking to Michael and he says he can build to support whatever we need to.
He's actually getting excited as everything is not new, he has straight walls, familiar corners and a normal roof. He says he was just overwhelmed with everything being different.
Is there a wall thickness that is optimal for thermal mass. Say with earth is 8" or 12" or 24" the best thickness for thermal mass. Michael says he can probably put 6-8" inside with serious support underneath or more outside. He would probably remove the metal so we would have roof, floor and studs to work with.
What would be the best material for thermal mass?