"Engagement" on YouTube typically means likes/comments on your videos.
It is well understood that the YouTube algorithm treats engagement as a significant positive signal to recommend your video to non-subscribers (or even, with enough traction, on the home page).
Not to my knowledge. Youtube's analytics generally don't give computed magic numbers like that, they give information like "number of comments per minute when the video released" or "average watch time" or "ratio of likes to views".
The exact way these numbers are combined in the algorithm isn't revealed (and I assume is ever changing).
It is well understood that the YouTube algorithm treats engagement as a significant positive signal to recommend your video to non-subscribers (or even, with enough traction, on the home page).