I use the 24 grits for everything. I dont by mulitiple grits because if I did, as soon as I ran out of one of them., I would simply use the others until they were gone too instead of stopping and driving to my jobber..
You absoltely dont have to do as I said, I simply offered up the suggestion.. It was presented to me years ago by a professional as a quick efficient way to strip panels.. I do them all that way now..
As soon as the paint and prime are pretty much gone, move on.. Then finish off the panels with 80 grit on a DA.. It will clean the panels the rest of the way up and get the metal prepped for epoxy