Hi there,
I've seen many different students and have myself experienced different things when it came to this. I was doing 5 A levels Maths, Further Maths, Physics, Chemistry and Biology in Year 12 on too of Olympiads, extra competitions and lots of extra reading as well as sports If we place whether or not it's advantageous aside which is a whole another conversation, it really depends on the person on whether or not it's hard!
I had 5 A* predicted grades but I later dropped Biology so I was down to 4 A levels as I wanted to prepare for my uni admissions tests and not have any regrets from taking a 5th a level which would compete for my time. I personally found 4 to be a huge weight off my shoulders and 5 to be a fun challenge, in hindsight it may or may not have been wise to have kept the 5th.
3,4,5, or even 6 A levels is all possible and have seen it done well before but it's a all a matter on you personally, how much time it takes you, the grades you're getting in them, uni application time, and also subjects! Many essay heavy subjects or coursework heavy subjects may take much more time physically get through the week!
Best of luck with it all! Only you can truly decide if you find it hard! feel free to DM for any specific details!