12.5- in my school everyone did maths, English lang, English lit, 3 sciences, 1 language, 1 technology (although there were exceptions to the languages and technology if you really hated them) and 3 other subjects, plus optional short course R.E.
I go to a Grammar school but even so I'm not sure whether its a good idea to push everyone to do so many subjects. I nearly gave up D.T because I found the coursework so time-consuming and I seemed to be always behind with it, I struggled with it, got really good marks in the coursework and didn't know anything in the exam (we weren't taught any theory) so got an A overall, whereas I got an A* in everything else. Still worth the stress I guess, I enjoyed it sometimes.
I also did Music early in year 8- although that sounds like I'm showing off or geeky, I don't think GCSEs on their own are very hard at all, without much homework or coursework or of course other GCSEs to revise for I just carried on learning pieces in my lessons, composed 2 or 3 pieces and didn't learn much theory but got 50%-odd in the listening exam and an A overall.