If anyone really feels like putting the time into it, they can potentially get all of the characters up to level 20 since, once the hack ends and you pick a route, the hack resets you back to Chapter 1-5. This also leads to potentially infinite Talismans, Secret Books, and Speedwings among the rest of the special weapons.
Then again, that would be cheating for when the rest of the game becomes available, so I won't be doing that.