Ok well lets sort out a few things first such S what do you have done so far and what size your main sprites are as most artist like to know how much work a developer is putting in before they contribute a great deal of time to drawing for them.
Also it is good that your leaving the art style mainly to the artist but it would probably be better if you either made a style the artist will copy and simulate throughout the game or give a few samples of how you want your game to look, like a comparison to another game in terms of detail.
While it is good to give the artist creative freedom its still your game and your vision as a developer that will need to mold how the game looks.
Also, A short exaple of the story can help the artist aswell get an idea for what you might like in terms of sprites.
Hope this was detailed enough for what you'll need to do before artists such as myself come to help you get your game going.
Have a great day
-Parker.