I see you ductaped the M4 so you can put it in the case. heh. but won't that block the cpu fan?
PC lookin nice so far.
installing to the X should be very easy. You have plenty of room in the back.
I have a Frontier and there's no room for it besides under the passenger seat.
as for display, stay with DoubleDin, single din screen will bump the top where the cig lighter is. Unless you can find one that can stick out 2".
here's my simple setup