I'm not 100% sure on this because it was a while ago when I did mine and rules change, but I think you used to be able to do the test with all exams completed except the RT practical. But regardless I would say it's much better to have them all done beforehand anyway.
How long it takes top book will depend on the aircraft and examiner availability at the club or school where you are doing it, for me it was about a week.
As far as tips go, probably nothing that you haven't heard before. Try to relax, don't stress about things, and if you make a mistake don't dwell on it because everyone makes mistakes and you are allowed to make some. A lot of people find it helpful to think of it in this way; You have already passed the test at the beginning of the day, the examiner wants you to pass and your job is just to make sure you don't change his mind!