Seren - guess you'll find that out on parent-teacher evening!
When you give a lot of homework it will always be a quality-quantity dilemna. I have to say, my school seemed to have very optimistic estimates for the time some pieces of work would take. One teacher got fired after the parents of a whole class complained after she set 5 hours worth of homework for the next day, then put anyone who hadn't completed it to her standard in detention...
Every teacher thinks that their subject is the most important, and that's part of the problem, and I think it is actually those who want to do well who suffer the most, as they end up spending hours on it. Throughout school and university I studied and ran, and did very little else (including not much eating and sleeping). My Masters year was a relief - I said I was going to do the 40 hours I was supposed to be doing a week and no more, and I ended up doing far better than in my degree because I gave my brain and body a chance to recover from the studying. I now study part-time, and am still working out how to get the balance fitting it around work, and managing to train as well, but I'm starting to settle into a routine.
Regarding A levels, do three "proper ones" and do them to the best of your ability (we all also did general studies as a fourth, but this requires no studying). In the rest of the time, do things that are of interest to you, and give you other goals/achievements/make you a better rounded person. This was my sixth forms policy and it worked: they have some of the best state school results nationally. We also all had to do one extra curricular activity which we commited to and was put onto our personal timetables, so everyone had something other than grades and wider reading to write about on their personal statement - be that a sport or a hobby. All of my school friends went to a different school. One of them got an Oxford offer, but then he screwed it up because he spread himself too thinly by being poorly advised to take four A levels, and ended up with AABB, when he needed AAA, which was silly of him because he got As in the ones he needed for the course (maths, physics) and not the totally unrelated ones (history, music).