Cool progress

I only just checked it out but the sketch this is based off of has good construction although it could be fleshed out more.
The helmet shading is flat and not consistent. Moving the highlight there towards us is the easiest (but cheapest) way to correct it.
Should I make the robe appear as it is being blown by the wind? If yes, how strong should it be?
Again, it's whatever makes the most interesting shape. See the difference between the last edit I did and the original.
Sketch a few different robes on top of your current sprite, try to find a good composition. Don't forget the torso underneath it.
BONUS: also do 50 studies of capes and drapery

Seriously though, if you recognize your weak points now you'll be struggling with them a lot less even after 10 studies.