Everything is more or less public. Subscriptions stay between your server and the server you subscribe to in theory, but you'd have to trust those servers not to leak anything.
Possibly, but it would have to be so severely locked down that it makes more sense to have a web interface with a few buttons that do some very basic actions, including making my phone ring or stuff like that.
In case anyone's wondering this is what we instance admins can see in the database.
In this case it's an obvious example, but this can be used to detect patterns of vote manipulation.
Would give me the name of the communities to give it a try?