Think of it as a car.
Sand to remove as much as possible, without penetrating beneath the metal, dust off, wipe with paint or lacquer thinner, prime, sand, prime, sand with a rust inhibiting primer, sand, remove dust and paint.

Do the process in a single, consecutive time frame.

Better yet, have it blasted with walnut shells or a similar media(even fine sand is too coarse) and use an automotive primer/paint.

I've used that paint before---the finish over rust was terrible. It sometimes worked, sometimes not.

A wire brush the size of a large toothbrush is better than sandpaper.

I just answered your identical post on the painting forum.

Thank you so much for all the responses. Very helpful!