If you ever wanted to get rid of masto.host, you'd be stuck with those old posts littered with those URLs, and your posts wouldn't work on the new server easily without mangling a lot of data.
I'm on Leo Laporte's server, and he literally moderates it himself... He says it's easy, as he just throws anyone problematic out, but, that's still work.
Also if this keeps growing, there will be "Moderation as a Service" kind of business for a fee. They would work for small communities. Waiting a bit, and letting enthusiasts to join existing servers is probably wise.