wow, thanks for such a thoughtful critique.
To answer your questions, it's a galaxy 8.0 tablet. We were driving home from Cedar Point, and I was going to go back to quickposes and do some more gestures, and then my daughter asked me to draw her.
I spent about 1 minute or so on the gesture then probably another 2 hours on details and cleaning up (I did the final lines on the same layer as the rough sketch and had a lot of erasing to do) and just generally messing with it trying to figure out wtf I'm doing. Contraposto is one that i'm pretty comfortable with even though I made a lot of mistakes. The rest of the time I spent trying to clean it up and fix the details. You're not the first one to mention that the proportions are messed up. I also posted it on /ic/ and they said so too, but that my lines looked good.
Even though the lines are smooth now, when I drew it, my lines actually weren't confident at all. I spent probably an hour with the eraser cleaning them up. Manipulating line weight is something that's new to me, so like you said, it's pretty haphazard. I just have a vague idea that nearer things, things in shadow, and intersections should be thicker.
Are you really a professional artist? That's really cool. I just decided to pick this up as a hobby, cuz it's embarrassing to not be able to draw any better than a kindergartener.