Commission and client agreements - what is being delivered, when payment is due, what happens if the brief changes, and who owns the result once it is handed over.
Setting up on your own - choosing and forming a business entity, the registrations that follow it, and the record-keeping that keeps it in good standing.
Rights in what you make - licensing avatars, worlds, models, textures and music, and what a commissioner is and is not buying when they pay you.
Terms, policies and the awkward situations - service terms for your own storefront, and what your options are when a deal, a client or a collaboration goes wrong.