Amps are cake to install... you have to decide WHERE to install them...
If you can install the amps under the rear deck in that wasted space, that would be your best bet... That way they are out of the way - just be careful where you put the self tapping screws!
Smaller amps can fit under the seats too.
Speakers in the headrests, doors, and some small 6 1/2" subs in the rear deck would be nice...
If you do headrest speakers, you'll want to put some small bypass caps on them to keep some of the real low and real punchy bass off of them.
My take on it is that the installation should show NO wires and should be invisible to thieves looking in windows.
Run the power wires and speaker wires down the channels under the inside edge of the carpeting under the doors and run the RCA audio cables under the center console (you'll need to make a small cut in the rear finish panel to bring them in under it) to keep them away from the power wires, brake light wires, etc...
I'd be happy to help if I could find the time. I have a large amount of crimp connectors and Molex connectors for my Spec project so don't go hog wild buying tons of connectors... You can get fuse blocks, connectors, wire, wire guides, etc... at Tanner's pretty reasonable. No need to spend the LARGE amount of extra money on gold plated everything. Those things are worth THAT much more money in my opinion.
Get heavy gauge power wire and thick speaker wire - don't skimp on those, but no need to put in Monster Cable or other pricey stuff. A good, flexible, heat & abrasion resistant 16 gauge wire will be more than enough for door speakers and short runs to rear deck speakers. 18 gauge works just fine for headrest speakers. Any thicker and it may show up all lumpy under the fabric. As for the amps, go for whatever gauge they use on the amp... or slightly bigger. Nothing smaller than that and no need for 4 gauge or something bigger...
RJ