The images at 7:17 which is compared to an earlier Hubble image is pretty nuts.

I know where i'll be getting all my puters background and screen saver images from in the coming decade.

JWST super high res images can be viewed/downloaded here
https://webbtelescope.org/news/first-images/gallery

I'm staggered that with so many places as critical points of failure--the JWST got through all of them. Amazing.

I know she says the "spokes" are the result of the hexagonal shapes of the mirrors (six sided mirror; six spokes)--but--does someone have a simplified explanation of why that's true for me to grasp onto?

You're absolutely right, my comment should have targeted the live launch, sorry.
Still, that covers about 20 (shaky cam) seconds of the launch before they switch to an animation (!) of the launch.
Which brings me back to my original gripe: The Ariane 5 is an old vehicle which doesn't have onboard cameras. Private rocket launch companies have eclipsed it. And I think The European Space Agency is not keeping up.
As to cameras on the JWST itself, it looks like they didn't attach any for a reason: https://www.space.com/james-webb-space-telescope-no-cameras-reason
Didn't know that...

It might help to start with what the Backplane Pathfinder actually is - it's a non-flight replica of the Webb telescope’s center backplane (that link has more info and pictures).

Chamber A allows simulating the cold environment the real telescope will face in space, and is the same vacuum chamber where Apollo spacecraft were tested.

Now, to answer your question: They are testing the test procedures for the real telescope! (source: NASA). I realise that doesn't exactly answer your question, but I haven't found details of the actual tests they plan to run... so as a distraction, here are some more images - http://jwst.nasa.gov/images_backplane.html

This stuff always makes me feel so small, but for some reason I can't get enough. Very excited for the JWST when it finally gets up there.

The thumbnail image for this video has been updated - thumbnail added by eric3579.