First, let me say that is a good, solid starter paint gun kit. You can get good results with that. Second, never say, How badly can I mess that up?" LOL That's like saying, "What could possibly go wrong?" Seriously, just take your time. Be careful and don't rush.
I totally agree. I just don't know if he knows what block sanding is. No offense,
@74Scooter, but when someone says they have never painted, I won't assume they know about block sanding.
When I block sand, I use a Dura Block sanding block and dry PSA (sticky back) sandpaper. I agree with the 180 or 220 before the primer on the fiberglass. I usually do 220 followed by 320, but the high build will easily fill 220 sanding scratches. Use a cross hatch pattern when sanding. If you don't know what that is, a quick Google or You Tube search is in order. Then spray the high build primer with a 1.8 or 2.2 tip. I also agree with Wayne0 about blocking with the 400, in that I finish with 400. After spraying the high build primer (any good 2K polyester primer will do), I block it with 320 to get rid of the orange peel, switching to 320 to smooth it out and ending up with 400 dry. Then I wet sand with 320 and 400.