I haven't been to the PPP yet, but from what I hear, the crowds shouldn't be too big for a couple reasons. For one, ticket sales haven't been as high as Disney would like, which is why they are planning a revamp for this event. The other reason is that you're going to the World at a great time, between Easter but before the schools have let out. We really like going during this period because the crowds are thin, and the weather is beautiful!
As for the fireworks, I personally am particial to setting up my tripod almost right behind the Partners statue, to get the straight on shot. Our last trip however, my friend wanted the best view of mainly the fireworks, and a cast member recommened a spot towards Adventureland, because when you're in the hub the castle actually blocks a lot of the fireworks. Your idea of Tomorrowland would be good as well, for the same reason.