As for the hair spec, I would suggest the Marschner model:
://www.cs.cornell.edu/~srm/publications/SG03-hair.pdf
Followed by the Kajiya-Kay model, which was just recently used by “The Order 1886” very successfully I think:
From page 33:
://www.gdcvault/play/1020162/Crafting-a-Next-Gen-Material