I ended up doing 3 A2s and 3 ASes (Long story), but I'd say about 3/4 A2s is really enough to meet any possible Uni offers - you don't need to do any more than that, as it was (for me, at least) quite difficult to do 3 A2s - you start to feel the pressure of the various subjects a lot come exam time, so I don't think there's really much value in taking the 4th or 5th subject.
I'm going to study History and Politics at Southampton this coming year: I got ABB in English Literature, History and ICT respectively, and got 9As and 1 B at GCSE.