I watched a Youtube video showing how a professional game artist, Magdalena Dadela, uses Substance Painter to paint the face of her characters and then used her technique to paint mine. Here is the result so far after 2 hours (see screenshots below). The eye lashes and hair are yet to be created and will be using separate meshes. To get the head and eye meshes into Substance Painter I exported the low polygon head and eye meshes from Blender as a single FBX file and then exported the high polygon head and eye meshes as a single FBX (I duplicated the low poly objects and turned these duplicates into high poly objects simply by adding a Subdivision Surface modifier set to do 3 subdivides upon “render”). I then started a new project in Substance Painter using the low poly FBX file and baked the maps except for the color ID map using the high poly FBX file.
In hindsight I should have exported the hair and eye lash meshes along with the head and eye meshes to save me from doing it next. Note: the curvature map turned out to be faceted rather than smooth until I changed the curvature baking algorithm to bake Per Vertex rather than Per Pixel. See bottom screenshot for this setting.
For the eyebrows I downloaded an eyebrow alpha texture from the Internet and made it square with GIMP and then imported it into Substance Painter as an “alpha”. Then I stamped the alpha onto the face.
The eye iris was done with an eye material built into Substance Painter.