I was working on the project, and now the character selector is complete:
Captura de pantalla - 201112 - 14:11:50.png
As you see, the selector is a "stripe" with all characters available, that scrolls left or right. I did it that way because it was simpler.

Also I've added a stage selector.

Finally, I was designing the inners of the "arena", that is, the objects and how they work together. It's quite simple but complex at same time, and I'm a bit frightened about it. I don't know why, but I am.