Hi Hannah. In my opinion the best advice is simply to do subjects you're going to enjoy. In reality you'll never have to use mathematics much beyond GCSE anyway and the other technical subjects involved in triaining arn't too in depth there is just a lot to learn. I think a language is a fantastic idea, always helps to be flexible when looking for work. You seem to know what you want to do so do the subjects you'll have fun with, give yourself a back up plan and keep the pilot study going as much as poss throughout your A-Levels.
Best of luck.