I just did my G8, for the first time, last week. It really wasn't that hard or scary. I was obviously worried to start, but I just taped up anything i felt would catch excess product, i.e cracks, slits, seams, vents, black plastic, etc.
As for the hood vents, I taped around the seams, but i did polish the top of them. They did just fine. The hardest places will be the front wheel flares. It is tough to get that sharp swooping angle. Make sure to tape up the sidemarkers and GXP badges. I know the clear coat is soft, but dont be too worried about it. Just ease off on the pressure on sharp edges or the peaks of curves (like on the hood or rear fenders)
The GXP front fascia is different than my GT so I dont know if there is enough paint to warrant using the PC if by hand. I have too much plastic on my mine to risk use the PC.
One more thing tape off the roofrack rails. They SUCK to get wax or polish off.
I dont' know the color of your GXP, but if it is black, one thing i found is not to use too much MSW. It will take forever to get off, i.e. it will leave dark blotches which require a lot of elbow grease to remove. But it you do get them, dont worry. Just make sure to use very little product and put it on evenly and very thin.
That's about it!