Wow. That's cool. You have bad power (the lighting bolt). Those screens take some juice as does the pi. The power-supplies (plugged into the wall) have been the biggest challenge in using those screens. You might want to power a (fused) 12V to 5V regulator directly from a switched battery connection, that way you can turn it on an off independent of the ignition to avoid bad power-up/down. And (I think) you can power it directly using the GPIO, bypassing the on-board regulator -- I do that for Arduino all the time, but I'm not sure if I've ever done it with a Pi.)
HALT: I use the adafruit code for an 'off' button from one of the GPIO pins. (sudo git clone git://github.com/adafruit/Adafruit-GPIO-Halt). Easy as pi:-/
Are you planning to strip down the OS to run ONLY the necessary code?
Aside from the power-up down & boot-up complexity, the next issue you'll eventually run into is that those pi's don't last forever. Eventually it will probably fail. (I've probably owned at least 100 pi's, I teach kids linux as a hobby. Failures are not that uncommon.)
