I love Dr. Barbara Oakley! It's a brilliant course. If you loved the course you'll also like a book called "Make it stick" - it's evidence-based, applicable learning science.

You're the smartest 16-year-old I know. Keep practicing the habits you enjoy (especially piano + writing) and you'll find yourself living a life of ultimate career freedom.

In case you want to improve your writing check out Nicolas Cole's book "Online Writing" - his biography might also inspire you for the steps you take after finishing school :-)