All you need left is to use different types of brushes for different surfaces. Mainly if you want to use textured brushes for shading. The reason being is that people looking at the art will see patterns and make assumptions with those patterns. For example, the hair is shaded with the same texture as the hat, so someone looking at this could assume the hair is also some sort of customary dressing, rather than hair. If you went full cell shaded then that wouldn't be an issue but its textured brushes that can misinform the viewer. Otherwise your character design and facial expression look nice.