I have created an art brush and a scatter brush so far but used only the art brush in my project. I tried to use the scatter brush but I think I need to work a little bit on that to make it look good.
I have applied the art brush mainly to the strokes of the shapes and to some lines in the designs and it's very interesting how different they look just with that simple change.
I'll try to do the pattern brush to add some shadows.
I have tried to add more texture, this is my final version: