Drywall touchups - ok after 1st coat of primer?

Yep. It's the preferred way of doing it. The primer highlights all of the imperfections in that "perfect" spackling job. I use MH Ready Patch or just the regular joint compound, depending on how quickly I want to get the paint on. Touch-up the primer to prevent flash through (when the paint sheen changes due to non-uniform substrate preparation).

Since paint is unforgiving of even small flaws, I noticed some divots and ridges on my new drywall after I started applying the first coat of primer. Can I apply some filler to the divots over the paint, and then maybe apply another coat of primer?

Please advise!

Use a shoplight to highlight portions of the work. This will help show up flaws.

charles