tip-never have one lead character, actually, never have a lead role at all. all players should be at an even field. The headmaster should not be a playable character given the supernaturally evil bit, either it should be your character, or just an NPC.
if any player would be given special treatment without good reason, it could be seen as a huge blemish, and if that specially treated character was yours (aka a lead role, not the evil guy, as that's generally fine)then you might seem self centered, putting your guy above the rest, making everyone else's character have no reason to be there.
so yea, it might be best to keep this as a 1x1, a group RP would most likely need to change far from your original plan to be good enough.
why did I say any of that....