Hi Elise! Welcome to ArtSchool! Your work looks pretty nice already. If anything, since I see mostly characters I imagine it's what you want to focus on, right? So I'd say definitely focus on anatomy. No matter what's your skill level it's always a good thing to work on if your primary goal is to draw people.
But really, I'd recommend that you start Artschool from the beginning and as you get a feel of the course, skip around to things that interest you more or that you think you need to work on. You can always go back to previous sections of the programs afterwards.