If you are planning to use the laptop for anything else, it may be worth looking into a docking station. Plugging and unplugging all those cables gets really old after a bit. You will also want at least one usb hub mounted where you can access it easily.
What are you going to power the laptop with? How are you going to cool it?
Your audio layout looks like a real winner, but the other items that make up your Carputer need some more looking into. Check out the guide, it is well worth it!