You can post to all of them you want, as long as they allow posting. As I've seen, some of them are "read only", which I assume they are mirroring other relays, although that might not be the case. I need to learn more about that matter.

I've basically added the ones I've seen that are run, used, or recommended by developers or people with a good knowledge of the whole thing. As I said, I don't know if that is even important at all, probably not, but I'm not posting such important information at the moment (I don't know if I'll ever do, haha), and we are just at the infancy of the protocol.