First off, Congrats!
All of this information is gleaned to what friends who have done the program have told me, I will not be there until August!
Vista is the loudest apartment. If you're into socialization, this would be the apartment for you. However, I have had friends that lived in Vista that are not partiers and they were perfectly fine. Vista is the oldest and it does show its age.
Patterson is the newest and most expensive of the three complexes (CPers can also now stay in The Commons, but I have no idea about those because they were just opened to CPers this Spring, so I won't talk about them, maybe someone down there now can say something about them) and it's also the quietest. Personally, I'm planning on staying in Patterson because it's newest and I like quiet. However, friends who have visited there have told me it can be too quiet at times.
Chatham is kind of a mix of the two. It's quiet but there's always something going on, so if you like to party and you stay in Chatham, there are still plenty of parties. It's also the same price as Patterson weekly. Chatham is more convenient because it has its own bus stop, while Patterson shared Chatham's bus stop so if you don't have a car, you might have to walk to get to the bus.
As for information about MEO, it is my understanding that you operate the turnstiles and are a greeter at the front of the park. You are the first face guests see when they get to Disney, and the last face they see when they're leaving!
I hope this helps!