you need a instruction manual of car monitor

19 inches is the largest size car monitor that you can buy.

Yes it can. If you have your monitor professionally installed you just have to turn the ignition part of your car on. If your power windows are able to roll down or you are able to turn on your lights etc then the monitor will work.

a rear view system set usually combine a monitor and a back up camera, so when car parking or car reverse,driver can see what is at back side of the car.

If your car have a monitor, no matter it is a stand alone monitor or a rear view mirror monitor or a DIN size DVD monitor, you can just choose a camera is ok.

If your car no monitor before, you have a lot of choice to choose, you can just choose a 3.5 or 4.3 inch stand alone monitor for back up view,or choose a 7 inch,9 inch etc,and also can choose a rear view mirror monitor.

Yes you can add a generic car monitor to any car but it won't look very good unless you have it professionally installed. Doing that will make it appear that its part of the car and will also be harder to steal.