I'm doing my AS levels at the moment and I'm taking three out of four of the subjects you've mentioned; maths, biology and physics.
You should be able to do well in maths if you keep up with the workload. At the beginning of the year I was getting Es and Ds because I was doing the minimum amount of work possible, but once I got into it a bit more my grades went up to B/A.
Biology is probably my favourite subject. The application isn't too difficult, but you really need to remember a lot of stuff. Our teachers have compared A level biology to learning a new language because of all the key terms and definitions. I find it helps to read textbook chapters the morning before the lesson so that I have a bit of an idea of the information before we learn it. It just helps to solidify the learning a bit if I'm getting told stuff and I've already done some work about it or have some background knowledge it before hand.
Physics is definitely the hardest subject I take, I would say it's a 9/10 in difficulty. However, I still enjoy the subject, and loads of my friends do really well in it.
I think as long as you're committed and dedicated to the subjects, and do maybe an hours work every weekday after school, then you should be able to do the subjects you want and come out with great grades. Good luck.