MESH IMPORTING FOREVVERRRRRRRRRRRRRRRRRRR

Hi. Subsurface, Solidify and Mirror modifiers must be applied before you import the mesh in s4s.
Once you apply them, you will see how high the final polycount is.
The ideal topology is not the one that is dense or shaded smooth, but the one that is optimal. The density should be higher in places where it is needed to preserve details or for the mesh to bend and lower where it is not needed.
The mesh should have back side geometry only in places where it is visible. Uncheck Fill Rim as well.

The hat chops should not be non-existent. If you do not want to make your hair compatible with hats, just duplicate the base and change cut numbers to 0000 and 0001

The hair is not weighted, vertex painted, has no uv_1 map. Do not import it in s4s until it is fully functional.