Sorry for the late reply!
What type of game is it and what type of art style are you looking for.
It is a four player 2D platformer & arena fighter. When it comes to the art style, we are thinking about something like Towerfall / Samurai Gunn, but a bit more detailed, cleaner look. We are very flexible though, and very open to suggestions from artists.
the size of the characters/sprites that you are willing to see in your game =)
The characters we user are 66x92 px, so around that size. As long as it retains the w/h ratio, then we can make it work.