I [created and] moderate !technicaldeathmetal, and since it’s a niche interest on a fairly small platform, it’s mostly a ghost town, with me posting music I like. This works for me in that I never wanted to mod anything, just wanted to join a community I ended up having to create myself. Though it does feel a bit like shouting into the void.
As far as rules, yeah instance rules are the baseline, then you can stack whatever you want on top of that. Idk how to grow, I’m making everything up as I go along. I’ve been posting regularly myself to put the community on metalheads’ radar, maximizing the variety to try to throw a wide net, cross-posting very occasionally (ok I guess once lol) to related comms, and starting themes (“Secret Killers” for hidden-gem bands, “Left Field” for established bands that haven’t made it big somehow, and “Mods Are Drunk Friday” for posting zany stuff that otherwise might not fit).