If i could make a suggestion, It should be Kei or Yumi if you decide to stick with protagonists' but if you decide to do the antagonists it hsould be Specter.
Now before you say something like, "why should kei and yumi be a separate character, they would just be clones, they should be alt costumes." think of it like this.
In Ape Escape 3, they have a morph system, which is the main reason why i think they should get separate characters, they would have alot more moveset potential with that. They can turn into like knights, ninjas, space warriors and all that jazz. they could be like Toro,if you will.
Level 1: they could turn into their wild west form, and shoot their net that travels a set distance
Level 2: could be the genie dancer form lol the genie causes everyone to dance and you must hit them while they are dancing
Level 3: can be their cyber ace forms, it would essentially be like Coles Level 3. They have a move that suck the opponent closer to them, they can shoot bolts, and if the opponents are like really close together, they have a move where they can dash into one opponent and it chains into the other ones that are close enough.
See? those supers sound might fine dont they?
Best part, Yumi and Kei can be alt costumes for each other. only you would have to have two voice actors if you so decide to choose one over the other
I'm 100% behind Specter for the sequel.
As for your ideas, I like this game having more stance-system fighters. Tekken is full of them, I don't see why we shouldn't do the same.