Good luck with this project! Try not to get sued!
I do have a suggestion, though. You mentioned that you want to wanted to add more classes. Maybe you could add a second class change as a side-quest? Also, you could give the player options as to what class to change into, sort of like Seiken Densetsu III. For example, at the first class change, a Fighter could change to a Knight (better defense) or a Gladiator (better offense). Then, at the second class change, a Knight could change to a Paladin (better offense, white magic) or a Guardian (best defense), and the Gladiator could change to a Berserker (best offense) or a Magic Knight (sword magic)... or something like that.
Let me know if you like my idea - I have a lot of other good ones, but this is your project!
