@LMAO is flooding the site with random communities because they’re salty about being banned for claiming too many community names. They claim they’re trying to “fuck your entire site up” but I imagine it’s a relatively quick fix to delete all the communities they’re creating, LMAO.
Nobody. Think of it like rafts on the ocean. The only policing that’s done is allowing someone else to keep a rope from your raft to theirs. If you want to defederate, you just untie their ropes and they aren’t your problem anymore.
An instance is a piece of server software, so you are spending your own resources running this software. It won’t have any effect on other instances besides showing communities that are hosted on your instance. No information is transferred until someone from other instances subscribe to your communities.