A satellite community of multiple such youthful communities is a win-win for all. That’s what real estate companies do, but they profit enormously from it with little value. They are building on top of existing infrastructure and not passing the monetary benefits of it and pocketing it for their purposes.
I am not being flippant because I have spent a few years on such a model. A community of 6000 can be supported in 600 acres that will actually not only be self sustaining but can also be income producing if you add farms and value added businesses for those who don’t wish full time jobs. There are monetary and communal benefits. There will be less reliance on govt and less wastage of resources.
120 is a good number because it would satisfy the Dunbar number limits. It shouldn’t be difficult to have a nice proportion of ageing, young and middle aged populations for diversity.
It’s just a modern tech supported version of eco villages and ..dare I say..cults. But they fail because they never take the necessary survival factor of monetary stability and most eschew technology. These don’t have to and will be better supported.