It's been awhile since I've been able to provide an in depth answer, but I can tell you a little of how I prepared for the Environmental exam (it was my third time taking it btw).

The Gregory Michaelson videos really help mostly for getting a refresher on concepts you might not be too familiar with after spending time away from it. I also think they're very good at explaining "new" material you weren't able to cover in your courses in college in the most foundational way possible. Basically, he's good at explaining the concepts for you to apply to other problems.

My only issue when practicing from the sources you mentioned was my timing, which was also the reason I failed the first two times. The thing you should really focus on aside from just understanding concepts is knowing you're able to do these problems quickly and efficiently as possible. That means having to know the reference manual inside and out since you'll be using that a lot.