Hi Jon!
Welcome to the journey and enjoy the ride

. The recommended way would be to view the videos and be done with your preparations before utilising the PM PrepCast Exam simulator to test yourself under simulated "real conditions". This way you'd have a better measure of your readiness for the actual exam and would be able to identify areas you may need to re-visit to understand better. What I did during my preparation, for each lesson, I first watched the PrepCast training video, then referred the PMBOK and other material on the same chapter and solved the questions related to that chapter. Took me two months to prepare for all the modules this way, due to my work schedule. In the final third month is when I spent the time to only take tests and exams such as the PrepCast Exam simulator to evaluate myself as to my readiness for the actual exam as well as to be able to identify areas which I might have to re-visit if there was a pattern of scoring low on questions from that module. Therefore I feel that leaving the PrepCast Exam simulator for the end (after all your preparation is done) is the recommended way going forward.
Hope this helps.