If there's half a dozen, you absolutely have to tell them something in advance. You'll be giving them no less than five "The Princess is in another castle!" moments, that's enough to make a lot of players just phone it in. You don't have to tell them everything or even the precise number, but definitely let them know "There's some champions you'll need to defeat, it's definitely more than two or three" or whatever because otherwise, there's a real danger that if by champion #3, they get told "Yeah... well, turns out there's another one" yet again your players simply stop caring especially if each of them is a multi-session plot.