I going to start with the PrincipledBsdf node in P12. I came across a Blender tutorial based on its PrincipledBsdf and each of the channels. I will attempt to explain the additional nodes as I go along. Note, I crossed out 2 nodes that I typically connect to the Specular channel on the PrincipledBsdf node, it is an IOR to Specular converter based on a Blender tutorial and specific to the dielectric material.

Whenever I use a character diffuse map, I try to find a comparable base map that contains no makeup or tattoos. In this particular case, I am using a character map from V4 and her base map that was originally included with her release ages ago. I use the base map as a subdermal texture map that is connected to a CombineRGB, red channel, and eventually connected to the PrincipleBsdf Subsurface Color. The reason I use the CombineRGB is to separate the RGB but yet have some control over what color is expressed by the Subsurface Color. I played with various combinations by changing numbers in the green and blue channels. Use your imagination. If I make a Star Trek Vulcan character, I can recreate green subsurface scatter because those aliens have copper as a hemoglobin base as opposed to humans that have iron as a base component. For a bump map, again I use an unblemished base map. I lifted the bump map nodes from EZSkin3 and bundled them into a compound node. If you like to see that, let me know.