I would do the same if I had a billion dollars or two to spare. The future is city states and networked small towns of 10k mixed population ..use the same seed idea as the Dunbar Number. Fwiw, I have already designed such cities for my own amusement with high density housing in 10% of the total land and the remaining as forests and food producing acres..underground tunnels for intra city transport and above ground, self driving cars and efficient public transport(maglev)…
it will be a three tiered city with skyscrapers, underground city and ground infrastructure. Etc etc.
What’s the point of being a billionaire if you can’t even build your own city?