If you're going on bare metal, my paint guy says 3 coats etching primer, 2 coats high build primer, then color.
If you put the primers on one after another, wait a few minute between coats per instructions. I'd do a very light sand after that, preferrably 24 hours or more later, then do the color.
You only need to sand if a significant amount of time has passed (see paint instructions). I've done several primer jobs after repair/upcycle jobs, but leave the final coat for the customer, so I don't have much experience after primer.
__________________
If someone tells you that you have enough bicycles and you don't need any more, stop talking to them. You don't need that kind of negativity in your life.