Hi Gordon

First step, take a deep breath and relax. Your research will pay off.
When you lay the cloth out on a bias you are only moving the cloth off a longitudinal plane by a foot or so.

So the cloth does lay on a diagonal but only as far as the width of the cloth will allow. Closer look at the video may show the cloth overhanging the boat is longer on one side. I do not bother with this myself, never had a problem that needed a fix.

The seal coat is a very good idea. It helps reduce potential problems during wet out of the cloth. I suggest you do this as a first timer. I will always do a seal coat.

Tip, make sure your temps are high, I like 80+ degrees and that temps are falling during your seal and wet out. Apply epoxy with a roller, pop bubbles with a heat gun, level and remove extra epoxy with a squeegee.

Wear safety gear

Robert, visionary