Wow using historical figures as Wizards to battle is a good strategy and I have the feeling there will still be more Surprise guests I'm sure.
Now I knew it would have been Hermione or Luna both being the two closest to Harry (Ginny wasn't til the later books).
Finally I think you forgot two important students/friends, the Patil and the Weasley twins!
IMHO the more the better!
dennisud