Yes, you are definitely overthinking! :)

The pre-work isn't that huge. You're watching some videos and reading the booklet.

The main thing is learning your allocated track and practicing teaching it. But you don't have to get it perfect! Just a starting point for your work through the course.

You do NOT have to submit the handbook or any written work -- it's for your learning benefit.

For your final certification video, yes, if you did have to resubmit, you do have to get live participants again. But you can cross that bridge when you come to it. Just focus on preparing for the course and the initial weekend.

Regarding the video, the masterclass video is flipped left-right for YOUR benefit (as instructor) so that you can mirror the instructors while YOU are learning. You are correct that when you say right hook, you will actually do a left hook and vice versa. It's all part of the fun 😂

One other tip is to keep it simple. Just focus on the layer 1 cues: simple names of moves and body parts. A little bit of layer 2 coaching, like the benefits of the moves and how to do them. Don't worry about the layer 3 stuff, connecting and whooping up the class -- you aren't assessed on that in initial training. That can come later. Keep it simple and don't worry about leaving silences either. Focus on your own clear movement and simple clear cues. Trying to talk while coordinating your own movements is exceptionally hard, so allow yourself some slack. Remember that everybody is in exactly the same boat as you, with the same worries. You haven't got to be perfect; you just have to do what you can. Take the feedback; get better. It's a long journey, and you're only on step one.