Hey Lewis!
Regarding the first question; Physics and Maths are the two main topics needed to be a pilot so with the others I would choose what you enjoy and what you are good at and also have a back up career plan, i've always said if I don't become a pilot I would like to join the navy as a seaman so I studied along those lines aswell as sticking to Physics and Maths.
At A levels it's pretty much the same, I'm doing Physics, Maths, German, English Language and Spanish. I would also advise you pick English Language as this helps in almost every job.
University wise, its not necessary to go to university to become a pilot however it is advantageous. I would strongly reccomend moving away from the aviation related topics at Uni as airlines aren't fussed what you have a degree in and if you study Aviation related topics and fail to become a pilot (Chances are decreasing due to the financial situation) then you have pretty much wasted a lifetime of education which is where your second choice career will come in. I would say study what you enjoy or are good at at Uni because at the end of the day, most employers couldn't give a flying toss what your degree is in, so long as you have one.
Hope that helps :8