The model and textures are from 3D Scan Store: https://www.3dscanstore.com/hand-3d-model/female-hands
First, I removed unwanted shadows from the diffuse texture between the fingers and created some extra maps for shading (cavity, thickness, mask for nails, micro detail map).
I projected the micro detail map with solid projection on the model and masked off the nails with group mask.
I used Color Correct and Color Gamma channel modifiers on the diffuse color texture to create epidermis/dermis/lower dermis color variations.
Nodes in Schematic Viewport
Thank you for reading.