Wow a lot of questions, not sure I can answer them all.
If you move from Tesco to Sky you WILL have to change your email address.
Make sure Sky broadband is available in your area. I enquired a while ago and Sky told me my area was not covered yet.
If you want Sky that you can stop, start, record that is called Sky+ (Sky plus)
We have multiroom and we have a Sky box in each room, and they are totally independant of each other. We can watch two different chanels in the two different rooms.
Note: I think you have to pay extra for a Sky+ box, and you definately have to pay �10 extra a month for multiroom.