My school only structured 5 options blocks (and hence 5 AS chpices) but it didn't stop me doing 6 - English Lit, German, Maths, Chemistry, Physics and Further Maths (the one I took independently). As long as you're committed, intelligent and also have a real knack for the subjects you're doing, you can do 5 or more no problem.
I still had time to do wider reading, complete my DoE, and do miscellenaous other things that filled up my PS quite nicely. As Isiash_Berlin said, a little time management goes a long, long way!