Aaron Davis wonders "when are you an actual ‘citizen’, that is when do you belong to, in or are a part of the Indieweb?" To me, "belong to", "in" and "part" signify slightly different depths of commitment, none of which conveys "citizenship". The way I understand it, citizenship is granted by some other authority. You can't just claim it for yourself.
I like Kartik Prabhu's idea that posting to a domain you own is all it takes. "Everything else is a bonus". But that's a little like Robinson Crusoe being a citizen of his island. Interaction with others matters too.