I plan on doing the same A-levels as you and an EPQ. I was considering doing another level, similar to yours of an AS level, in Physics, however, I have thought it's better not to do so. 4 A-levels and an EPQ is a large volume of work in the span of just 2 years and even an AS level would add a lot to your schedule, so you have to keep that in mind. Also, even though it's true that computer science skills are very desirable in the modern workplace, doing just an AS in it may not be very fulfilling as you will not be learning all the content. So, universities won't view it as highly. Another thing is that A-Level CS is definitely going to be harder than the GCSE, so you're going to have to put a lot of time into it and the other subjects you want to take are very taxing. Is it really worth it to sacrifice so much time to half an A-level whilst you're putting the other 3 at risk? If you really wanted to, you could do your EPQ on computer science and use an extension of your GCSE knowledge to write it. In my opinion, an AS isn't worth taking, especially if you enjoy the subject. You might be disappointed with how limited your topics will be compared to your peers, so in the subject, you won't be able to be as competitive as you may hope.