My goal was totally OEM looking, I don't have a single cable dangling or visible anywhere.
I put a raised floor in my trunk and placed my pc, peripherals, and 2 amps under it.
My car ( 2000 mazda millenia has a standard double din slot that I put the screen in. I'm running without a head unit.
For am/fm I'm using a $50 visteon HD radio module with a control cable from mitch on mp3car.
I use roadrunner with a custom skin to match my interior.
For GPS i've got a usb receiver and I'm using IGO8 PC version (its kinda free), I can't say how awesome this software looks and functions!!
The best $90 I spent though was the contour shuttle pro.
Contour Design, Inc. - Innovative Ergonomic products for your computer.
I have it programmed like a BMW idrive system, I can do almost anything from it without having to use the touchscreen, that lets me keep my eyes on the road and have complete control. My car had an excellent spot for it, right in front of my armrest, and it looks like it came there from the factory!
You seem to have most of the parts, the most important though, is to not use inverters!
Inverters are very inefficient and will introduce noise into your audio!
Carnetix makes some nice dc-dc regulators, with a laptop though it is tricky to control power on/shut off. I went microatx because it is cheap, available and powerfull. MB cost 80 cpu 80,ram 20 dollars and hd 80. Make sure cpu is low power, AMD makes some low power ones....
gota run, wifes calling, baby's crying...