So I've decided that what I need most at this point is to seek out formal instruction rather than trying to figure out everything on my own.
I've started taking a set of classes at the Torpedo Factory that involve three hours of sculpture in the morning, and then three hours of anatomical drawing in the afternoon; both classes work from a live model, which is an amazing opportunity. The instructor, Thanasi Papapostolou, is a fantastic sculptor, and the class was a real eye-opener with its instruction on how to render form and space.
While I feel like this drawing is a reasonable likeness of the pose, I can see now all kinds of things that I couldn't see before as far as ways to use hatching to create the illusion of form, and using the hatching to make certain areas recede, things that were not done very skillfully in this drawing; but I learned to look for those things in the process of doing the drawing, so that makes it a successful experiment!
I am realizing, too, that there actually is an enormous difference between working from photos and working from life.