I've done more fiberglass sanding than I want to recall. On flat surfaces you can use a long board sander on all other areas I use a rubber sanding block. Light guide coats of primer is a must do. 180 220 320 then final with epoxy filler primer . and sand that too. Unless you have a lot of experience with a air DA , I would not suggest using one . Lastly that stuff is extremely dangerous and you need long sleeves gloves, a good ventilation set up and a quality respirator mask and goggles.