1000 seems way more managable than any relay trying to become nostr's one biggest server. I'd say that's the best and simplest starting point - 1 relay per community.

The more complicated versions would be something like 10 relays that allow mixing of communities. So 10 people "ultimately in charge" because they own the relay and have the strongest decisions, with lots of smaller communities with different moderators and rules for what's allowed. This is a more difficult problem, but helps keep responsibility managable.

Communities have their own rules for posting, but still need to comply with whatever the relay operators' rules. If the communities don't like those rules, they can go to a different set of relays just like individual users.