I’d suggest only taking 4 A levels if 1 of them will be an easy A/A* for you. In my case, I took Chemistry, Physics, Math, Further Maths at the start of 6th form and later dropped Chemistry (when I mean later, it was about 5 days later). I have to say this was the best decision I made since I found myself focusing a lot more on my other subjects and saw my grades improve. If you decide on taking 3 subjects and is confused on which 3 to choose, you could always take up an additional subject to see which you enjoy the most and drop the ones you might not be as strong at or isn’t needed for your choice of degree.