Are you going all the way. Like with rear headrest monitors, separate video on all screens, high def, all out sound sytem, etc ?
Because that will be a major influence on what type of car/truck/suv you get.
An all out system IMO is best in an SUV. Now a system with engine monitoring, hvac control , multiple cameras, etc is more fitting for a sports car or sports sedan type of setting.
So what's the plan?