1.He is, for him in the movie, it's him being his old self and everyone's irritated he hasn't grown up.
2. Only Stiffler's Mom is in it.
3. Only the people who were in the first 3 American Pies were in it.
4. They actually have something about that in the movie. Won't say if they did or didn't, but you'll see something along those lines in the movie.
5. Honestly, I thought the movie was hilarious. Right now, I'd give it an 8.5 out of 10. I haven't seen the other three in a while so I can't compare right now. I'll say this, it was funny from the get go and was rolling with it throughout. Some characters made some crappy appearances though. Like it felt like they stuck them in there... just to be in there. I'm not going to lie, I feel nostalgic now and I'm probably going to rewatch all the movies... not the straight to dvd ones, the ones with the main cast only.