I'm installing the 50resto gray carpet right now, myself. It's not that complicated but there is a bunch of stuff that has to come out, like almost the whole interior. Take your time.
The 50resto carpet doesn't really have any holes cut. As far as the seats go, I just laid the carpet in position and felt for the bolt holes (for the back of the front seat tracks), used an x-acto knife to cut a SMALL hole. You'll need to do this b/c if not the carpet backing tends to wrap around the bolt as you're trying to thread it in. This procedure shaould be used for the seat belts as well. Like said before, just cut a small 'x' where the bolts poke through for the front seat studs, and for the stereo bracket under the dash.
Something else I did that might interest you. I noticed that the carpet insulation was kind of thin for the replacement carpet. I went to Lowes and got some of the reflective foil-type insulation that people used for there attic. It seems to make the interior quieter already. The reflective material should help reflect heat back out as well. I might get flamed for this but it should do the job well. It is thin so it won't raise up the carpet too much and it was easy to install and mould around the interior. I cut four pieces, one for each floor well. Also, it's not a heavy material, so it won't add much weight. I've also heard about dynomat (sp.?), and this it's supposed to be good.