I have spent some time going through the course at DNAcademy - it is great.
Michael Cyger is a cool guy, who we are really happy to have as a user and even happier that he is making money with park.io. He got the domain php.io on park.io for $1,655 a little over a year ago and flipped it a few months later for thousands of dollars in profit. I’m sure you also know that he does the Domain Sherpa show, which is full of great stuff and I listen to it every week.
I also met him at Namescon earlier this year - a genuinely nice and very professional guy.
But DNAcademy is great and I highly recommend it - I have been learning a lot as I go through the course. It covers everything and has a nice and easy interface so you can pick up where you left off. The forums are helpful and I’ve noticed some other park.io users posting there.
The cost of the course will definitely pay off, no matter what type of domain investor you are.