Depending on your client or UI, there should be a sidebar or something of the like that will list who the mods are, and you can message one or more of them from there. I’m not aware if there’s a way to send a single message that goes out to all mods of a community at once rather than messaging them individually.
As for #2, I think it has to do with how federation works. In my experience your subscription should still work even though it says it’s pending.