Sorry about the freeze :( I'll work to get it fixed on the next update.
Yes, you only get 5 characters at a time, Americo, Aguara and Alfonzo are fixed, but the other 2 depend on the zone you start on, so one needs to start the game at least 5 times to see all the characters.
Since you started on the Desert you got Fausto and Penelope, that were also in Rookie's Day, all the other zones have at least 1 character that wasn't on RD.