I actually don'T know if I'm the right person to help you for that XD My work tends to be rendered in a rougher way than you, so it's easier to ''fake'' the different materials's texure, if that make sense. Your work is rendered much more carefully, so I'm not completely sure how to tackle this problem.
With that said, I'd definitely try differents brushes with a little bit of texture just to see how that works. I know a lot of people recommend using a single brush as much as possible, but coming from a traditional background, I find Photoshop brushes pretty limited. You have a wide range of strokes and texture that can be made using a single brush in real life, but that you can't really do with only single digital brush. So don't go crazy by using dozens of different brushes, but a having a few different ones to chose from could potentially help.
Another idea may be to simply draw/paint the different textures on a different layer on top of everything and drop the opacity so that we see a difference in the textures, but that it's not too overbearing. Does that makes sense?
Hopefully that helps you in some way 
