Thoughts about 'The Prisoner of Azkaban'

I have now rewatched all three of the Harry Potter films. I can highly recommend the DVDs, especially for the numerous cut scenes included on each. Although you do generally have to leap through rather tedious hoops in order to get to see them, especially on the DVD of the first film where they are the reward you get for solving various puzzles. Great for hyperactive kiddies: merely irritating for adult film aficionados.

I have also begun reading The Prisoner of Azkaban, which is the first book in the series that I have not yet read. This, of course, means that I am reading it having already seen the film, so I have a couple of questions in mind which arose from seeing the film, and which I am hoping the book will either answer or, at least, illuminate.

Cuts follow for spoilers and rather excessive length:

( Question one: Sirius Black and Azkaban )

( Question two: Alan Rickman, J.K. Rowling and Snape's legilimency )