GCSE art exam recommendations?

[hw.]

Your idea sounds great! Personally I'd go for gouache because it's easy to ad lots of detail and that's what the examiners are looking for; if you prefer acrylic or oil then either should work fine, it's just that if you're using the paint provided by school then the paint might not be great quality, and personally, I think there's nothing worse than working with bad quality acrylic. It's up to you though! Try testing out whatever you like on some paper and seeing which works best for you.