A couple of your questions were answered by Rowling (http://today.msnbc.msn.com/id/19959323/) in a Today show interview today (and tomorrow). The MSNBC web version says what becomes of Luna. She also said that the Hogwarts headmaster in the future would be some brand new person rather than some familiar old character.

I don't think she's writing them thinking about the movies at all. If so, she's doing an obnoxiously bad job of it, from a filmmaker's perspective.