It sounds all right to me. What other cameos do you have in mind?
I do have one other idea, but I kinda dont want to spoil it at this minute. What I can tell you is that it's cameos from another game that's familiar/adored by people here, so I'm not just going to pick a set of characters from a game to be involved that no one here will recognize. Also note that these probably wont be human characters for the most part, since I feel animals/creatures fit more in a "Mario departs for a great adventure" type scenario more.
Happy to see you like my idea, though!
Mario's Greatest Adventure! <- My hack thread, where I make magic.