I'm standing by my opinion that selling the characters is not the good way to approach f2p for fighting games. I'd take the valve road: make the entire game free, and only sell cosmetic stuff.
With a fighting game, players develop a STRONG connection with their character(s): that's where you want to monetise. Make them try out and play anyone they like, and then, when they start to feel this "bond", sell them costumes, accessories, titles, quotes, stage entry and winning animations, taunts and what nots.
I would buy the crap out of stupid things for the characters I play.
This- DOTA2 model would work fine for a fighting game.