Hi there, I used your drawing to practice my shading Nohara's Sketchbook - #380 by ynr_nohara, couldn’t finish the other 2 unfortunately, tablet’s battery dying.
Great practice 
, also I think the first shadow pass is very important just as the flats (local colors). It determine the type of lighting and the position of the light source. Every shading pass after those 2 will follow the established information. At least for me, those first 2 are my top priority when I use manga process.