There are touchscreens with USB
7" is the standard you can get a lilput or a Xentec (not sure if thats the right word) they both just use a normal monitor cable to plug into the monitor out on the laptop then usb for the touch screen.
There are USB GPS available they are mostly a mouse looking GPS they most popular is a BU-303 altho it has problems.
You could either take the DVD drive out of the laptop and use a USB cable to hook it um to the laptop is under the seat and the dvd drive is in the dash etc.
There are adapters that take the 12v from the car and push it up to 20v or whatever the laptop needs. No need for an inverter.