FAQ: Power Supplies Explained (Part 1)
check there for help deciding on powering the system... sounds like youll need a good size DC psu but the power calculators will help you in that thread.
'00 accord p4 mobile
here is what one person did for a stealth project. search around and more will show since it has been discussed before.
For GPS: GlobalSat BU-353 or Holux GR-213 are top notch receivers... seems the BU-353 is a bit more favored and is sold in the MP3Car.com store.
hope that helps...