Clay Davis Drawing (Work In Progress)

Clay Davis from "The Wire" and his infamous catchphrase.

For a full view, check out: https://forrst.com/posts/Clay_Davis_Drawing_Work_In_Progress-FFH

This was a drawing I started back in January and finally got the chance to sit down and start coloring. This still needs a bit of work, but thoughts and opinions are welcome.

Right now (and I think forever) I drawing on paper with pencil, ink, and then scan. Colors done in Photoshop + Wacom tablet. What I would like to improve is my brush(es) personalization. The white, brown, and in between accents are made with a chalk brush from the Nagel series. Can anyone point me to a really solid tutorial to create brushes?