About the theme, you mean we all model the exact same character?
That would be easier to compare i guess but a tad boring though.
Maybe we could go for the same character but add a variabel like a weapon, transport, outfit or hairdo of choice.
I'll throw some ideas.
-Chibi vegeta with some devious weapon
-Model your own Dragonball online character
-Model an unexisting fusion of 2 dbz characters.
These are presuming the direction of the theme is dbz.
For me it's fine if the theme will be of another anime(don't know too many though) or even something completely different than a character of an anime.