Quote:

...I am still a little unsure the best way to sand primer in prep for first coat paint? literally.



This was mentioned earlier in the 10000 pages but bears repeating.

An old body shop trick is to use two contrasting colors, like a very thin coat of black over the gray primer, as a guide coat for sanding.

As you sand, the black paint remains in the valleys of the scratches and thus are easy to see to sand smooth due to the high contrast in color.

I'm not an old bodyman, so feel free to correct me If I got any of that wrong.