Wow, this sounds like an amazing project. Pipe dreams are the best, but easily accomplished when you have so many friends willing to participate.
I would say right off the bat that you should look for something to buy, it eases a lot of the responsibility of leasing someones land and gives you the freedom to do whatever you want--within reason.
Also, with so many people, I wouldn't bother purchasing prefab homes. They can be filled with toxic gick and you can easily build something so much more fantastic with so many people helping. Look into strawbale and cob construction and if you really like it then you and your friends can set up a schedule for building each others houses one at a time until they are all done. I recommend looking at the mud girls collective if you haven't before now to get inspired. https://www.mudgirls.ca/
I think with that many friends you could build something to share in a year or two, then spend a summer constructing reasonable homes for each of you.
Pick your location with care, find out what kind of building codes will need to be followed. Even if you plan on doing a composting toilet, you may be required by county laws to put in a septic tank. You may be required to install multiple tanks for multiple houses.
Many small homes can curtail a building code if you build under a certain size. Or better yet, just build the main "shared home" with plumbing for everyone, a shared kitchen space and dining hall, then build individual homes as "dry" cabins without plumbing. Each of these would give the owner personal space, but be much cheaper and faster to build.
Sounds like an amazing idea. Go for it and post here to let us know how it is going.