More Pottery Questions

Spoilers for Deathly Hallows (which I loved), but not that much.

• What subject did Dumbledore teach at Hogwarts before becoming Headmaster? Wikipedia says transfiguration, but is that anywhere in the books?
• So...when exactly did Ron, Hermione and Harry pass their apparition tests?
• Is the wizarding world Christian? They celebrate Christmas, Mrs. Weasley says "Thank God," but it's not like any of them have ever gone to church...
• I still don't think Snape was truly good, despite the big reveal. If James Potter had been married to anyone else but Lily Evans, Snape would never have asked Voldemort to spare anyone, and never gone to Dumbledore full of remorse. He would have been a Death Eater through and through if it weren't for her.