I don't take art so I'm very much a layman from this area - take what I say with a grain of salt. I'm not trying to deter you here, but I think you should consider these two things:
From what I've heard from my friends I'd say that you'll need to be extremely skilled and able to work toward developing coursework using various media and vastly different styles. I've heard of some borderline photo-realistic paintings being given Bs, so keep in mind that standards are high (in my school, at least).
Another concern is the fact that there is a lot of work to be done. My friend (who does IGCSE Art and Design) told me that they had to do around 60 pieces of coursework by sometime in year 11. I don't know about the level of rigour at A-level but definitely brace yourself - especially if you're doing challenging subjects.