It's not *too* mathsy, like if you meet the maths requirement (usually it's a B/6) you'll be absolutely fine on this front.
Difficulty is so personal, some people are able to pick up programming with such ease whilst others will struggle the entire 2 years, the theory for exams though is generally not too bad, just get good at big essay questions really.
I'm sure there's a revision guide, your sixth form college will definitely supply you with books and such, but the spec really depends on your exam board.