I did five, or six if you include general studies
Maths, further maths, physics, economics and English lit, so not really easy subjects. Chosen for a combination of being good for what I wanna do and being what I enjoy. I got 4As and a B in English lit, for AS.
I don't want to do all 5 for A2, I think thats a bit too much so will drop English.
However for this year it wasn't too bad. Being generally bad at essays I did sometimes get bit stressed with the amount of English essays but I think I would've had the same problem if I'd only done four because if you can't do something, you can't! If you have no real problems with the five subjects you want to take, then you might as well try.
If you find its too much after the first month, term, or whatever, drop your 5th choice?
Do you have time in your college timetable for 5 subjects in the week?
I had to do further maths after school, but only because general took up a subject slot in school (had to do it). If it all fits into your timetable I'd say definitely worth a shot. If one would be in your own time/after school make sure you have enough motivation to keep yourself interested and doing the work when you have less teacher pressure.