Limit amount of sites per server, stop new sites creation on some servers

I'm wondering if it's possible to

1. Limit the number of sites that can be created on a web server, to prevent overcommitting a server.
2. Limit some users from creating sites on some servers, but allow them on others (to stop new sites created on old servers, while allowing an user to edit their old sites.

Perhaps there's a way but cannot find it