Multisite interactivity from artists

I am trying to figure out all of the great multisite plugins that I need for an interactive art gallery where users can post their own art according to art category: paintings, metal art, etc. I want to use as many appropriate plugins as I can and currently am using all except site maps, multi-db, and some others that I can't use or haven't learned how to configure yet.
My question is which plugins do I need to set up these art categories where users can post on these subdomains, subdirectories, or anything else appropriate? And, with the plugins you suggest for this, is there an order of priority on which plugins to setup/configure sequentially? Also, how do I assign certain themes to certain art category sites?
Thanks a lot.