I think you should clean up the line work, you should be able to improve the pose.
Especially the arms need work and also the head.
I would first lose the black lines on the inside of the object as it will just make it harder to shade it, just make it blocks of base colour and add shader afterwards.
One you have done that, you can use the trick (i recently redisovered) of selecting for example the coat with lasoo then press ctrl-h to hide the mask, and paint just inside the coat area with various colours.
This stops it from going outside the line work or his face etc.
Some people also use a separate layer under or over and play with blending options but I never really tried it out...