Cam power connections

Installing reverse camera on aftermarket head unit ... do I use power from HU, an alternate power from HU which my unit seems to have, or tap in directly to reverse light...and do connect to the positive or negative wire of the reverse light?

Is this the same pos or neg for parking brake connection and or other cams?

And what power does 2nd dashcam use for same system?

Could dashcam just be attached to 12v acc power on HU?

Lastly should I use the built in single thin red power wire (located on the video cable plug on cam extender cable) or power through cams pigtail plug with power and ground wires? TIA