The partner idea sounds fantastic! It might have some balancing/technical issues, but I absolutely love the idea! I would reduce it to to 4 partners for balancing, and have partners from the 1st two games only though. The rest of the move set is pretty good too!
let me explain because you can balance it.
How I interpreted the playstyle was that I viewed him as high control and versatile character that needs maintenance to adapt himself. What I mean by this is in his game, if you wanted to chnage your strategy, you had to risk soemthing. For example, switching partners make you loose one of your 2 turns (unless you ahve quick chnage, but let;s not go there). If you wanted to use a special moves that isn;t the standard jump and hammer or the basic moves from your partners, you had to use FP.
This is where the maintenance comes in, for example, I would put a laggy switch mechanic. The point is to have goombella defaulted so she is accessible, but weak. Switching becomes risky, but it';s a risk for havign the right move at the right moment. Making the switch diffcult, but the mvoes very usefull kinda allegiate the balance thing. You would ahve to find a way to switch like knocking far back the foe or soemthing.
As for smash attacks, same thing, I woudl expect power smash to be more laggy, hammer throw to be a bit less laggy, but weaker.....etc.....
This is where I think the balance would come in