You dont ‘take’ degrees in university the same way you take A level subjects. At one time, you study only one degree. First you do an undergraduate degree, then you do a postgrad. For now, pick the A level subjects you vibe with most and think is most useful for you. Don’t feel that you need to take certain A levels for a degree you may or may not do in the future, esp if you wont enjoy them. At the end of your A levels, you can decide if you want to go to uni to do a degree in a field which takes what you learnt in A levels, a step further. Or do something completely different, it’s up to you.
As for how many degrees people do, it’s up to them and their own personal circumstances. For example, you can easily do multiple undergrad degrees one after the other, or do what most people do and do one undergrad followed by a postgrad. After completion, you can choose to do a postgrad (pg certificate, pg diploma, masters, phd, etc) if you want to and if you think its useful for your career development.
I can give you my example. I did 5 A levels in English, Maths, Physics, Chemistry and Biology. I have almost finished my MBBS medical undergrad degree and I’m currently doing a Masters (pg degree) in genetics. In my case, I would have done 1 undergrad and 1 postgrad degree. I’m planning on doing another postgrad degree, but thats cos i’m a mega nerd and you certainly dont need to do this.
An undergrad degree can last anywhere form 3-6 years, depending on the course (mine is 5). Now I’ve seen some people say that degrees are split into modules and semesters, but this isn't always true with all degrees and it differs from university and courses. In any case, that isn't something you need to worry about until you have finished A levels and are thinking about UCAS applications.