Escapecraft

Do you have to do anything special to register / lets the mods know about a town, or does it just count as a town if you build it that way?

You just build it as a town.

If you want to, you can post in Lord's settlement post so it's added to the list. But that's optional.

I'd recommend that thread. If there are any issues with that town I look at that thread. If your town is not in there I go by default server rules.