Unfortunately, I don't seem to have the controls in your item #1. I've attached an image. The settings on the left is from the Teams web app, which is missing the "Devices" tab. The settings 2nd from the left is from the Teams desktop app, which has a "Devices" tab, but the "Camera" section doesn't have an option that enables automatic camera activation. Descending into "Open camera settings" shows some hardware calibration parameters.
Regarding item #2, that is what I do now, but I sometimes forget due to hecticness.
Regarding item #3, I am not in control of policies that control camera settings (or policies of any sort).
I appreciate you weighing in anyway!
