Chael,
I was in a similar position to you, deciding which A levels to take a few years ago and settled on a similar selection (maths, physics, and computing, with further maths chucked in there for good measure and guaranteed thrills
). Having done all of them, I can't really say that at the A-level stage any of them are particularly relevant to being a pilot. You are never going to need to differentiate, know about Poisson distribution or up and down particles or write an entire computer program at FL390. Most if not all of the theory that you will need to pass the ATPL exams and operate on the line, you will have already covered at GCSE level, except perhaps a tiny bit in (the equally thrilling) theory of flight. So I slogged two years to sit back slightly in one lesson for one hour.
That is not to say don't do them! If you are good at them and enjoy them go for it; they will increase your confidence in those subjects, and will give you a deeper understanding that can only help when it comes to the pilot exams (which are predominantly maths and physics). What I am saying is don't feel as though you have to do those subjects just because you want to be a pilot and that job sounds a bit computery and wingsy and calculationy so they look about right. It would be better for you, and probably for your CV to do A-levels that you enjoy and you are likely to do well in than to feel as though you must 'fit in the box' and not achieve as high grades compared to if you did something else.
With regards to what licenses and in what order they come - look at the bottom of
this page, follow the timeline, and click the buttons for more information.
Hope that helps!
WP