[Zeke]

Pookie, most painters will use a solid base of factory paint and any decent repaint. Any pelling paint MUST be eliminated. If some of the paint comes off with the hose, may I suggest that you try to remove as much as you can that way. Man, if water could remove everyone's paint, life would be much easier. No chemicals, no blasting. Once you are satisfied that there is no more loose paint, a through degrease and dewax is next. Do not sand a car that has any grease or wax present, you will just sand the wax down into the paint. Sand as mentioned above and prime. Epoxy is good, so is polyester.

You asked about how long you could wait before priming bare metal. Most painters prime any bare before they go home for the night. Depends. IF you have a warm, dry shop, you might be able to start where you left off the next day without prime. Don't paint over rust.

Most of the painting process is preparation. Lots of block sanding. Going over a car willy-nilly with a DA is a good way to ruin everything. I use them sparingly to blend in spot repairs. I mostly hand sand, dry or wet, with a block. Shows up every flaw.