They look very good! What you could try doing is drawing the sides of the box that are facing away from the 'camera'. That way it would be easier to visualize where the spine connects to each block.

Looking good! I'm still going the course as well but here are the mistakes I see: Make sure the "soft mass" between the ribcage and the pelvis really connects and interacts with them, on some of them your's look like a silhouette that you slapped on afterwards; which undermines the structure.