Psyk said:
I think it's pretty much only Oxbridge that will look at your GCSE grades when you apply. I don't think any other universities will really care if you have decent A-levels. Saying that I really would aim for at least 5 A*-C grades. A lot of colleges/sixth forms won't let you do A-levels with less than that. But the point still stands that it's not really important which subjects you do.
That really depends on your course. For Medicine or Law (at top unis) or something, you will need very good GCSEs. However, the OP should be fine with 5A*-C grades as you said.
As others have said, your GCSE choices are not that important however, I would go with double science just so that you have a wider choice if you change your mind about your future. I orginally had similar plans to you but have applied for an Electronic Engineering degree. It would be extremly hard for me to get a place without A Level Physics (impossible at most unis) and to do that, you usually need GCSE Double Science. Just in case it helps, I will give you some of my experiences with my GCSE I choose:
French: I hated this subject. Probably because only 3 people in my entire year group picked French so in order to have a decent class size, they dumped everyone who didn't hand in their choice forms into our French class therefore the majority of people didn't care about the subject. I also sucked at it. Somehow got a B but decided that I definatly didn't want to take it at A Level. I now regret not carrying on with it. Foreign Languages are also very useful in many careers
Business Studies: I found it very interesting. I didn't really find it that difficult either. I wouldn't say that it is particularly useful for IT or even Business though
That was the only choice we got (other than double or single Science)