Both Unreal and Unity have modes for examining this, and other bottlenecks. For example: https://docs.unity3d.com/Manual/OptimizingGraphicsPerformance.html Are you writing your own renderer?
that should depend on the hero and their material settings I think. What hero are you doing? I know for example Vengeful spirit's specularity is INSANE
I think the sixe of the head is fine. With heroic characters like this small heads are always used to emphasize the muscular body. A good example of this is of superheroes.
Looking great so far! Could use a large gradient overlay to draw the eye to the middle of the bow. For example http://wiki.polycount.com/wiki/GradientMapping
I think there does exist the concept of a vec1 value. It's a 1-dimensional vector. Something like just an X coordinate, for example. Their length is their value.