Oh well, the first two are quite simple ones.
1. Can't see, why you cannot apply for the catered halls, do they explicitly say, that you can't do that? Even if they ask you to leave after the 31st week, you can ask them about summer accomodation in some other hall.
Yes, there is a large catering facility in the Streatham campus, they have several departments there to satisfy different budgets. You've heard probably about the taste of the local food? Finally, you're getting used to it. :) I'd say the prices are from 3.30 for the main meal and down to 1.50 for a burger and chips. And it's the cheapest - cheaper it can be only if you cook yourself.
2. The choice of the residence depends of course on what kind of life you prefer. Lafrowda is the cheapest and the largest hall and it's down to earth. There is a student night club the Lemon Grove - "Lemmy" - right in front of the residence, and a lot of partying is going on even inside the halls. If you're aiming for a quiet life - choose James Owen Court, St David’s Brunel Close, Northernhay House or Bonhay House. They are also building a big residence on the New North Road, I'm not sure if it's already open for booking...
Personally, I'm staying in private accomodation, the price is the same usually, but much less people in the house, and much quieter. There is a link http://www.exeterstudentpad.co.uk/exeter/Accommodation-Search.asp
If you'd like to choose the private one - go for the St.Davids, Pennsylvania, Central Exeter or St.Thomas areas. Sometimes there are amazing offers in Horseguards. The funny thing is, shortly before the term starts, there are veryexpensive and rugged, but immediately after the start the number of offers increases and they are all cheap and good.
3. Sadly, can't answer this question, I'm not doing any courses here, I'm doing PhD in physics, it's mostly research.
If anything else interests you, ask away, don't worry to appear bothersome. ^_^P