I've seen VH's with the head unit in the glovebox. I think it can be a good idea, both for security reasons, and because it keeps a bit of originality about the vehicle. All though for everday use and convienance, it's probably not something i would do, but that's just my personal opinion.... As for the wiring, i can post a diagram for you, closer to when your ready to begin the install. Would first need to know what your installing, and whether you will be adding external amplifiers, ect..
But before you begin, what's your budget? and what are your overall expectations on the final set-up.
I'm going to go out on a limb here, and suggest a little bit different of an install..
Firstly, i wouldn't be cutting up the door trim's, particularly on a VH, and if it's in good nick.
Rather than installing a set of 6-6.5 inch speakers in the doors, i'd spend a little more, and get a good set of 4 inch speakers, to replace the factory units. Match them up with decent 2 channel amp, and possibly look at installing a set of coaxials,(again, budget pending) in the rear shelf, and have them running just off the head unit.
Then look at adding a good quality 10 inch sub,(or 12, depending again on your listening styles ect..) and amp.
All up, will still provide you with good sound quality, without sacrificing too much space, and you'll retain much of the factory look of your interior.