The way my auto body instructor explained a DE VS an Orbital sander (like a Jitter Bug) is that both the DE and the Jitter Bug make little circles, but the DE also makes Big Circles so it removes material faster But also leaves a different scratch pattern.
While not all of the DE of my day would do it some had a lever and turned it into a Mini Grinder.
Back in the day self stick adhesives were just starting to be offered.Before them we had boxes of circles of various grits and we would spray the pads and stick a circle on it.
My DE and my Board sander were both Hutchins and they didn't take a lot of air, however some of them are air hogs. I hope your compressor puts out enough SCFPM so that the blaster and the DE will operate properly. Remember Standard Cubic Feet Per Minute is different than Pressure. I believe this is what my little compressor puts out: 5.0 CFM @ 90 PSI; 6.0 CFM @ 40 PSI Back in the day, if I'd tried to use my Binks to spray a car with the Binks would have run the compressor to death. These new High Volume Low Pressure guns use an enormous amount of air. You may be able to run one to apply primer but I'm not sure.
Before you use the blaster on the test sheet metal, be sure to use your hands and feel the surface for smoothness. Believe it or not, those cheap brown cotton jersey gloves can actually help you feel imperfections that miss with your bare hands.