A:AnswerYes, it will work fine as will any Canon EF lens. Since the 80D is a crop-sensor camera (as opposed to a full-frame sensor), you will end up with the equivalent of a 160-640mm lens. That means you'll actually get more 'reach' from this lens than if it were used on a full-frame camera.
A:AnswerYes it will. BUT, this is a powerful lens. Buy at least a mono-pod (one leg tri-pod). The lens needs light and obviously is better out of doors. DO NOT USE IN HIGH DUST AREAS. Think about this, when you pull the zoom out air has to enter you lens from outside. That needs to be dust free and noncorrosive.
A:AnswerDepends on your lighting, but I can't imagine any issues outdoors. I was shooting today at iso 400 and with a shutter speed of 1/250 and had no issues. And, the image stabilization on this lens is fantastic.