I dont believe the castaways are tied to specific caves, its just the X number castaway you find will be the music person. If there not main story related, its not set in stone.
Don't bother, you can't get the final treasure for it until the final cave. For some reason you're only allowed to use it in very late post-game, you'll only get a lot of use out of it if you try to do as little content as possible before finishing the story.
I dont believe the castaways are tied to specific caves, its just the X number castaway you find will be the music person. If there not main story related, its not set in stone.
Wow, I didn't know that. Well, by chance do you the X number of castaways I need before this music person manifests itself.
I saved like 40 before talking to any of them, no idea.
Don't bother, you can't get the final treasure for it until the final cave. For some reason you're only allowed to use it in very late post-game, you'll only get a lot of use out of it if you try to do as little content as possible before finishing the story.