How long should I wait between sealer primer and sanding primer?
The type of paint you are using should have a spec sheet. With PPG they are called P-Sheets and they tell you the times.
If you are sealing metal it's normal to do you body work over the sealer. This might be useful:
https://www.e-bodies.org/how-to-paint-a-show-car-step-by-step-guide/
Thanks Cody. That's a good link