I'm sending in my application form at the end of next week, after getting it checked on Friday. For what it's worth, I think:
1.20 Tick the box about doing the test, and enter your test confirmation number as well.
1.21 to 1.28 I think they're being very nosy here, if you know that you have no claim to British nationality through your parents. I have the info ready, but I will ask when I get the form checked if it is really necessary.
2.4 The notes say 5 years, but if you only need to be here for 3, then who knows? For me this was really easy, since we've been at the same address for the last 12 years.