1. Nope, I didn't. In fact, I never announced it. x)
2. There is a Gossip protocol, in which relays and profiles - and the combination of them - get spread across relays to increase discoverability. In other words, some relays eventually spread my information, and thus my relay, around, and it was picked up by some clients. I think it's called "Better App", but there is a specific Nostr client that uses the gossip protocol to connect to some relays depending on a set of rules.
3. I haven't really thought of that x) But I will probably limit to either a register-first (= auth) mode, or limit it to just myself. Not sure, but I am far from having to figure that out yet. o.o
Hope it helps!