... and I don't know the correct order in which who to play as. In other words, who do I play as first? I'm thinking Ventus, then Terra, then Aqua. Please, tell me if I'm wrong, or if there's a better way to play so that it's more understandable.
That's the way it makes sense story wise. Unless you want to be confused like crazy. Aqua's story has the most story reveals since she spends most of the game observing what Ven and Terra are up to. I only played it for Braig.