Hey, from one ambitious student to another
For reference I did 4 A Levels and an EPQ and have recently started studying at uni after taking a gap year. There's a few things to consider here.
1) I haven't actually heard of a college or sixth form allowing you to do 5 a levels. This is because each subject requires something like minimum 6 hours teaching which which 5 subjects is a 30 hour week, plus you need time for essays, homework, research etc and to do non-academic things which also are needed for your personal statement e.g volunteering or sports. Personally, even if you had the choice to do 5 A Levels I wouldn't reccomend it. 4 is impressive enough without compromising your social life or happiness (and trust me on this one because A Levels are a lot of work) plus no university actually wants or needs 4 A Levels, its just something for yourself really (for me it was because I liked all 4 subjects and also kinda wanted a 'backup subject' which I knew I was better in, in case I wasn't as strong in the others.
2) Saying that, if you want to do 4 A Levels and think you could handle it, go for it. Expect that its going to be tough but if you put in the effort it will be ok. I would say I think doing 4 mathsy subjects or 4 essay based subjects can make your life a bit harder so think carefully about your choice. But also don't forget if you are struggling you can always ask friends or teachers for help, or even drop the subject to an AS Level or even drop completely. It's important to remember that even the most prestigious UK universities only want 3 A Levels (admittedly all A*'s) but just put it in perspective because obviously universities would prefer 3 really good A Levels rather than 4 or even 5 okay ones.
3) For reference, I took Computer Science, Economics, French and English Language. That worked out as 3 essay subjects and one more mathsy subject which I think was a good balance. Also, I think it helped that I already had taken french gcse and was fairly proficient in speaking, reading and writing from about 9 years of practise before I did the A Level so I found it much less demanding than my other subjects.
Im not going to lie and say it is isnt kinda cool to say I've done 4 A Levels and an EPQ and it is a great thing to put on your personal statement and CV and in job interviews. Just bear in mind the workload, know when you've had enough and take breaks when you need it because it is a lot of work and you can't just sprint to the finish line.
Hope that helps. Let me know if you have any other questions I might be able to answer. Good luck