What attracts me to the character is that the dark mysterious vibe.
As usual, I start out with scribble lines to find the pose. Then I established shape or silhouette and along the way I also try to get the lighting direction on top of it. When I figured out where the light source is coming from, I will establish basic value all around the painting. Once I have the basic value in place or close, I will then refine it more and make sure that it is as correct as it could be. Then I will start apply color and paint over the value sketch.
As for using custom brushes, do not worry so much about what kind of brushes I am using. Just focus on what kind of edges will the particular custom brush produces. There can be pretty much three types of edges from using your brushes, not more. Custom brush strokes can give you hard edge, soft edge and lost edge so you have to know how to utilize them. Thought there are custom brushes that will give you like a stamp on result like tree brushes, leaves, etc. Those are totally in the different category because they will give you actual silhouette of objects.