1. Does the radio function properly when you just turn it on using the ACC (pressing the push start button once) without starting the car?
No, Stereo is turning on, But screen and controllers other than volume key buttons are not working.
2. Say now you are playing a song or listening to radio somehow by keeping the car in the reverse gear. Now you put it into D. Does the music continues, or the system goes totally dead?
Yes, Music continues, and only volume key buttons are working. Screen turns off and no other button is working.
3. Does the camera work?
Yes, Camera works, But not turning on automatically on reverse gear, I have to go to the audio system menu and select the reverse camera.
Sorry for not being specific in the question. Do you have any clue?