It's a very expensive retrofit if your car wasn't fitted with a TV tuner when built. The tuner alone is around £850
This company can advise on pricing and parts required. Have your Vin# handy. TV / Rear entertainment
As above, it can only be viewed whilst the car is stationary unless you break the law by hacking the system.
No........if you want to explore getting TV added to your car, call the number for Comand in the link I posted and have your Vin# handy to give them.
That way they can see exactly what you have fitted and what you need.