Hi!
Please note that I’m going to move this thread across to the Community Events forum as that seems like a better home for it – however the URL should stay the same and you should also remain subscribed to any updates 🙂
When a submission takes place, regardless of whether the event is new or an update for an existing one, the tribe_ce_before_event_submission_page action should fire. You could definitely use this to add your own code that tests to see who the current user is, and query to see how many events they have already authored – then take appropriate action from there.
Does that help at all?