Oh, hows this:
We have a rotating turn when one of us(for example alphabetically, should be easy. I'm sligthly dyslexic though) gives idea, character, theme and off we go.
Giving our interpretation of it.
Deadline would be a week normally, fortnight(2weeks) for challenging or original stuff. In effect : on monday theme/character/idea is given, by next sunday(or one after it) we see what we came up with.
This would be besides the usual sketches, ideas and what-not's we post and want to create.
Does it sound like a deal?
My suggestion for a start: make one of your favorite characters, own or borrowed.