Radio replacement, yes another one.

[Mort]

🤯 replacing the current all singing dancing dose everything ( in Japanese) audio unit, falling apart fed up listening to Radio 2, Caroline. 

All sorted but I need some info on stuff before I plunge down the rabbit hole. 

Rear camera: shop thinks but not sure that camera format won't match new unit,Pioneer. Not the voltage issue but will only give a poor view. Not bothered about front  cameras. 

Speakers: is it just a case of counting speaker grills to work out if it has surround sound? I have numerous handbooks and certificates for the system but all Japanese. 

Any help will be appreciated. Ta muchly