I'm not a big fan of Captain Toad being DLC, at least not when we have what we can assume to be a limited number of "newcomer slots." Mario technically got nine new characters as well as a returning cut veteran, whereas Zelda's not really had a new character aside from Toon Link since Melee, and Wario has been generally snubbed for the idea. If we got 10 characters in all, I'd like
Mewtwo
Lucas
Roy
Ryu
Wolf
Dixie Kong
Chorus Kids
Toon Zelda (ideally Tingle)
King K. Rool
And after that, my wants would basically be limited to seeing a second rep for Wario and Punch-Out!!. And as for Isaac, I'm not really pulling for him, but I'd be happy for other people if he was in.
(Also I took out Inkling because I felt that she could stand to wait until a later batch of DLC or until a sequel)