Honestly, I'd advise against art as an A Level particularly if you want to go into a stem-orientated field. Art is a coursework-based subject so there's a large volume of work needed to be produced. If your school has an art club I'd suggest joining that instead as it will allow you to express your creative freedom without making it feel like a chore. If you really want to be a tattoo artist when you're older you probably don't need an art A Level as it generally comes as part of an apprenticeship with a licensed tattoo salon. You are right by saying that most STEM subjects at university only require 2 STEM subjects (Maths, Bio, Chem, Phys, psychology etc) though it does depend on the course on whether psychology is counted as one. For example, for Medicine, you generally need 3 Stem subjects from either Maths, Chemistry, Physics, and biology at AAA. While difficult, it is achievable if you really want to do it. Nobody really knows what they want to do after GCSEs but really you should go where your logical side thinks is right.