5 subjects is absolutely doable, don't worry about it. I did five and got good As in all (History, Spanish, Politics, Maths and Economics) and still had plenty of spare time for a good social life etc. (In fact I was freer than most of my friends because I just never bothered with homework until the last minute, suffice to say I did a lot of rushed essays lol)
In terms of getting good results, it's not difficult to do 5 A-levels, so don't worry. The only thing you should tell yourself is: "is it worth it? Do I really need it?" Because I didn't, and with a terrible clash in my exam timetable I ended up dropping Economics yesterday -- not because of the workload, or the grades, but because 5 subjects are not needed.
I hope that helped a little bit!