Welcome to a non-return valve in the pipeline of flying. Once you turn yourself upside down or point your face at the ground on purpose, most everything else in flying will seem tame and verge on the pointless.
First off, there is no "course", regardless of what the AOPA may tell you. Aerobatics is a lifetime of learning and trying stuff out. Getting some training is defintely the way to go but there's no aerobatic rating or sign-off or anything like that. It's mostly governed by common sense and the limits of you and the airoplane you're flying. You can take an AOPA course if you want, but it doesn't actually mean anything other than a structured approach to learning the basics.
To fly in airshows you need to have a Display Authorisation (in the UK anyway), issued by the CAA after doing an oral and flying test with a Display Authorisation Examiner. But if you haven't really flown any aerobatics yet, I'd suggest that's a goal for a year or two away yet.
Get yourself hooked up with an aerobatic instructor like Alan Cassidy at White Waltham or the folks at Sibson in G-WREN and find out what it's all about. I'd suggest if you're serious, aim to compete in Standard level next year as a real learning experience and a way to give your flying focus and purpose. I did that and it helped immensely in learning how to fly in a particular bit of airspace and make it look good to the ground.
Drop me a PM if you want to discuss further. I'm always willing to help out a n enthusiast!
Cheers,
Pitts2112