You really do not need to use a DA polisher, at any stage. Polishing gelcoat with a orbital polisher won't leave swirls or holograms.
Tips I've found helpful over the years:
1) Be careful around rubber/decals/sharp edges because the heat from the pad can melt them.
2) Wash the pad a few times during each stage to keep product from building up
3) Let the machine do the work
4) Hold the machine at an angle against the surface (look up a video of someone polishing and you will see what I mean)
Start on an area that wont be seen to get the hang of it