ML W164 NTG2 replacement?

[Ianmway]

Hello,

I'm sure this has been covered before but the Thread search function is not working so I'll post the question again.

I have an ML500 W164 2005 with a NTG2 (I THINK? it has video & AUX buttons, picture attached), without rear view camera fitted, I believe the camera was a factory option.

The advise I'm looking for is do I add a rear view camera, Viseeo MB-3 & some sort of DAB solution or purchase a new Seicane head unit, as here - Android Mercedes-Benz Car DVD GPS ?

I have 2 main questions;

1. If i replace the head unit what may stop working IE the analogue clock is set by the NTG2, is there anything else that may not work or be able to be set?
2. If I add a rear view camera to the existing NTG2 what do I need to do if anything to show the camera picture when reverse is selected?

Thanks

Ian