When I'm not sure what to add, sometimes that means I'm done - at least for now.
To me, this drawing looks complete.
But what matters is whether it looks complete to you.
When I have that "what is next?", feeling, I sometimes have to step away from the piece for a week and return with fresh eyes.
When I return to it, it's about 50/50 whether I feel like the piece is just done, or whether I have a feeling that something is missing.
If I feel that something is missing, sometimes I know what it is right away, and sometimes I have to think about what is missing for about another week.
Either way, this is a great piece already!
I would love to see an update if you do decide to make one, too. I enjoy these glimpses into other artists process.