Hello there,
There is no need to do 4 A-Levels since you only need 3 to head to university. Doing 4 A-Levels can further showcase your academic ability but I would only do it if you can manage the workload, since ending up with A*A*A will be better than BBBB. You could always take 4 then drop one in Year 13?
If you decide to go to university, once you get your degree, your A-Levels won't be looked at by employers since your degree would be your most recent, and highest, qualification.
Hope this helps.