And how do you see the damage done / taken.. in numbers or percent...for enemies,followers,and self.?

The only thing I've seen is, if your follower has been hurt, if you center the cursor on them, a red hit bar will appear under their name similar to yours which will disappear when they regain all their hit points. As far as what their level is, I don't think there is a way to tell other than they will be the same level as yours (up to a level limit of 50, I think) when you first acquire them as a follower.

Use wabbajack on them to turn them into gold pieces, and as you pick up the gold pieces count them and what ever the ammount is was there level.