Well the reason might be because, The game is normally only capable of loading up thirteen costumes because Wario used that number for his WarioWare and Overall costumes. (Even though it was only twelve costumes. I don't even know why Sakurai had decided to have Wario be the only vBrawl character with alternate costumes.)
That's an improvement on how many costumes I got. I had 12 costumes set up one time for Link. (Four being Brawl Link, Four being PM/Oot Link, and Four being SJS'/SS Link.)
Melee Zelda and Oot Zelda are different characters? Isn't Oot and Melee Zelda one and the same like Melee Link and Oot Link, or Melee Ganondorf and Oot Ganondorf?
Okay, just thought of telling you that, so if you'd go over the limit and the game starts freezing, you won't have to wonder why it always crashes at the CSS.