Hi Drew,
I personally work DG 501 a little more than wax but less than polishing. I can tell you from first hand experience that it is possible to over work the polish. If I recall correctly I used speed 6 on my PC XP with firm pressure and left Honda paint striped like a tiger. I would suggest maybe speed 4-5 at most and between 3-4 passes. It is safe to work the whole vehicle at once but I highly recommend inspecting each section before moving on. You don't have to follow up with anything for 5-6 months if you don't feel like it. I do but I'm usually going for max protection.
Two people on this board can give you more tips if needed, Richy (richy) and Sal (sal329). Let us know if you need anything else.