Sorry for the late reply everyone, I've been totally wrapped up in some other work I had going on.
Thanks for all the critique and advice, guys! It's been super helpful so far, although I've been having a rough time making a silhouette that looks "right" to me.
I'm not done yet, but this is the first few stages of my second attempt at it. I went for something close in shape to my original reference, trying to make it not too close. I'm trying to use the reference for help with lighting areas, as well.
Initial outline:
With first light shading:
With first dark shading:
I'll finish it up tomorrow and post the results here.