As far as I'm aware, most unis care about you're GCSE English language and maths, and only to the extent of you getting above a 4 in both, other than that they couldn't care less. Definitely include any impressive coding achievements on your application, that's a good way to stand out. But when your school tells you that things like EPQs or DOE or GCSESs make a difference for UCAS, they're basically just lying. In reality, if a uni cares about any of those, that should be a red flag for you.