Well, I'm not artist so I'll just throw some idea like Nomodae :
Peoples like to know what they're getting into.
Knowing the setting of the game, the style, amount of work you need ... Also knowing what you'll want draw (some artist may not want to dot scat / guro stuff for exemple).
Also, while some artists will be ready to do some free work for a free game, other will want payment.
And last of all, there is the artstyle (some get better with some game, there the question of taste too....).
You'll need a minimum of info to attract answer.
Plus, the fact that you, yourself, seem not certain of many of theses answer gave the feeling that the game project haven't been think through yet - so there some (big ?) chance it will no be finished, hence even less answer.