Finally, here is the full tutorial on Arnold rendering a photorealistic portrait in Cinema 4D with C4DtoA.
Although based on the kindly shared data by the Wikihuman Project, the workflows shown can be generally applied to improve skinshading on other characters as well.
Final rendered images can be seen on Artstation: artstation.com/artwork/WGAEQ
The additional assets used in this course are available to download here: uglykids.org/arnold.html
Thanks to ZBrush Artist Phil Amelung for providing the eyeballs, help on the texturing and facial hair creation.
I decided to provide this free of charge, yet if you feel like it and you enjoyed this, be sure to head over to uglykids.org/arnold.html and donate, so I can eventually record further clips.
You need the alShader Pack by Anders Langlands to follow along.
Enjoy the ride and happy rendering!