In addition to what Browno noted, you can evolve 3 star characters to 4 star characters to make progress for getting 4 stars. Additionally, we'll be adding more character inventory expansions, so this should be achievable without doing anything dastardly to existing 5 star characters you have (even if it will take a while).
My apologies, but our communication hasn't been consistent with that. It is correct that the Halloween event location doesn't count as a secret location for the various achievements that care about those.
So long as you have an email/password (or Facebook account) associated with your save game so you can log back in, you'll want to go into your settings app and clear data for the game. That'll force the game to redownload all of the extra data cleanly (but I think will also ask you to log back in again... I'm not 100% on this, because I don't have an Android device).





