Looking good for starters 
Here´s an addon that is currently being developed and I assume will be out pretty soon for cleaner shrinkwrapping of ready-made topology: https://blenderartists.org/t/semi-automatic-retopology-tool-prototype-2/1169338
Looks really promising
Also Wrap, which is a very professional standalone tool with many many features has a free trial worth checking out:
https://www.russian3dscanner.com/
My own workflow would most likely be:
1.: Use keentools for baseheadshape
2.: Sculpt secondary forms (eyelid creases, node and mouth creases, proper ear anatomy) on top of that with dyntopo or currently still ZBrush (Sculptris pro mode, which is almost the same as dyntopo in Blender)
3.: Manually retopo using RetopoFlow addon (currently 3dCoat, since Retopo Flow isn´t ready for 2.80 just yet) I can more quickly retopologize a face than properly set up existing topology for shrinkwrap, that´s why I would do it like this.
@Weekend: using vertex groups for shrinkwrap modifier would indeed be worth a try! Especially around the eye area and the ears 