608
Bluesky hits 20 million users
(www.engadget.com)
This is a most excellent place for technology news and articles.
No.
But they don't need to be. They're essentially just indexers.
If two relays index all the same content, then any services using either will be "interconnected" in the sense that any users can see each other and interact with each other.
Each relay host can choose what parts of the network they want to index, and as far as I can tell, any services could use multiple relays if they like.