In addition to the already good suggestions, I'd say give yourself a lot more time playing around with RHEL (or FC). Install it, configure it, break it, fix it. You will need to know everything in the exam prep guide
like the back of your hand -- another $749 ain't cheap if you don't.
I know you've explicitly said you do not want to take the formal classes, but if you should happen to change your mind, I was glad I took the RH300
class (which has the exam bundled with it), FWIW.
Keep at it, and best of luck.