I think that now, since we have a better idea of our limitations, I can think of better ways to make the game better:
-Having a lot of characters isn't really how to make a game better. What we should do instead is make sure is character is really fun to play as. Since now there will be more attacks on each sprite sheet, we will be able make each character more fun to play as.
-Adding a lot of extra content would probably also make the game last longer, but we do need to have good gameplay as the top priority.
-Like I said before, adding new, free content often will also help the game, as it will keep people hyped for new characters, arenas, and game modes.