Ok. I think I can help here. I shave my head with an electric trimmer (which I recommend getting, about $20-30 at Target, Walmart, whatever), and started trimming everything else earlier this year. (and no it won't grow in thicker. Otherwise I'd still have a decent amount of hair on my head :-)
This is what I've learned. First off, assuming that what you get comes with "guards" start out with the largest one (#4 or whatever) until you are sure both of you will like the results.
Trimming is easy. It took me awhile because I'm pretty hairy, but just keep going over the area. Figure out which way the grain is going, and as long as you're just trimming, go against it. If you're shaving, go with it to avoid ingrown hairs. Just park yourself in the bathroom (or someplace with tile) and go crazy. Sweep up afterwords. For me the only problem was me chest which itched like crazy for a week the first time. And that was after using conditioner on it! Nothing else itched at all (well, my balls did a little. But a little conditioner on the hair and it wasn't a problem). And my chest only itched the one time, so after the first time it's been good.
If you're thinking of shaving everything...take your time. That's a hell of a lot of surface area and it's areas that we, as guys, aren't used to shaving.
If you have any specific questions, feel free to drop me a line.
I don't think I could shave everything, without some persuasion, but I'm very happy that I started trimming.

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"A man talking sense to himself is no madder than a man talking nonsense not to himself." - Guildenstern, “Rosencrantz and Guildenstern are Dead”