Compared to Further Maths, Maths is a joke, particularly as AS level - it's basically just A* GCSE stuff in C1 and then extension of that in C2 (if you did Additional Maths, you've done most of it anyway). Further Maths at As is not too difficult, if you have good maths skills then you should be fine - you just do two applied modules and then one further maths module, which is pretty straightforward anyway. Physics is not too much bother either, if you put the work in you'll come out well. Computing is the only one of these I don't do, but from people that do, it is apparently more difficult than maths and physics and the exams can be tricky too.