I like that roster a lot, but 6 Pokemon reps with two of them being trainers with three Pokemon each. That's a lot.
I'd go with Pokemon Trainer Red (Charizard only) and Pokemon Trainer Girl as you described.
Edit: Also, I'd prefer Mewtwo to have his mega forms as final smashes even though it seems redundant and unoriginal given the other final smashes already described but it makes the most sense --- Charizard for SSBU Friend Safari: Grass Type: Sunkern,Petilil,and Quilladin
Same as Brawl except Mewtwo replaces Lucario. Mewtwo would be faster and less floaty than Melee (but probably still more floaty than most) and I would not have either Mega evolution, because I despise Y and X isn't really worth having either. --- PSN: TheUndying84