It's a beautiful vision. It also has the same concerns as
cob house, earthbag dome, log cabin, etc, which are:
1) Code. How are you going to get a barn up to code?
Answer? $$$$
2) Insulation. I expect insulating a 100' x 70' x 40' barn will be quite pricey.
3) Plumbing/sewer.
Compost toilets?
Humanure? See concern #1.
In addition to those things it seems like you'll have an extra concern with keeping rodents/roaches out and also you'll essentially have to build a house inside the house to get the rooms/upper floors.
I commiserate with you. For years I have been dreaming about an earthbag dome house. I would never get it past code here unless, just maybe, I got an architect's stamp on it to circumvent the code office. That will be very expensive unless I come the party already prepared with very detailed floorplans/plumbing/wiring/etc. I can't do that unless I have
land picked out with a site plan in hand. Around and around I go.
Incidentally I have some
experience with what you are attempting. In the 70's my dad, sister and I built a huge barn on the top of a mountain in the blue ridge mountains. It had a stream for water. Our family was going to live there. But lots of things happened. Hornets got in and stung my dad a million times. Despite having a large
wood burning stove inside, the interior was frigidly cold in the winter. He ended up selling the mountaintop and we moved into an A-frame.