Re: Missing the most important question
The biggest problem with rotating number plates is that you'd have to remove at a minimum the supports behind the bumper, and possibly cut a hole in the radiator on most modern cars.
Ejection seats are pretty easy to add, just shockinglyi llegal and prone to disaster on the MOT when the tester tries to adjust the seat when moving the car. Just ask Martin Baker for a couple of zero zero ejection seats. Jets deal with the roof by fitting explosives in the glass and blowing them up at the start of the ejection sequence, and I suppose you could do this with a car. Although there is a good reason pilots wear armoured helmets....
Caltrops are dead simple, just a door dropping a box worth of them.
Machine guns behind the side lights is not impossible depending on which calibre you want. The higher the calibe the bigger the problem and the fewerr ounds you could reasonably have stored. The biggest problem is feeding the ammo in and ejecting the empties. Much easier on older cars that had more space in the engine compartment or something with a rear mounted engine that has the boot space up front.