im not fully sure but i know that most uni's require maths and further maths or physics as course requirements to study computer science, as opposed to computing alevel as computing alevel covers very basic theory (like the gcse) but check on uni websites!
best combination is computer science, maths and physics (and further maths if your doing honour's pathway)
ya that can work,, computing alevel isnt mandatory tho and physics isnt required either but computing alevel is good for coding experience and background knowledge before studying at uni