hey, thanks for writing,

first thing i did was block in the base colours roughly, before also roughly blocking in the darks. I usually do this with big simple shapes and zoomed out so I can see the figure as a whole, keeping me from losing myself in unneeded detail. Then I go in and go over segments individually, rendering everything fully.

you are correct, there are two light sources, the one from the left is dimmer but also plays a bigger part in defining the 3D form. the second light (rim light) source acts to make the figure 'pop out', and can help emphasize the silhouette. There is also a little bit of reflected light around in the darks.

hope this helped!