hey Joel,
There's a saying around these parts. "You can only two of three things in an artist: expediency, quality, or cheapness."
In other words, the best scenario you can hope for is an artist who does quality art but takes a year

. I...actually am not exaggerating.
I highly recommend that if you want to start a project that you actually pay your artists. If you can't pay now, wait till you have the money saved up to do so.
If you're not 100% certain that you're willing to pay just yet (and you can) free work can be done...but for short 4-8 page works. It's impossible to ask for more unless you develop a personal relationship with the artist, which takes a lot of effort in itself and can take time to even find such an artist (took me 30, no joke). Now I find that paying for my art will get me the results I need for longer projects that I can make money off of, while non-paid work is only good for practice and for submitting for anthologies and publishers...trust me on this, and even then it's quite hard to motivate the artists without in depth explanations of the work on the forum. Not the whole bible, but you're going to have to do a proper elevator pitch leaving out nothing.
I understand that this might seem unfair, but art is very intensive and even if it weren't, you're asking for a lot of work more than likely with nothing but the artist's passion. To inspire an artist to put in 100's of hours of work is possible of course...but again, if you expect very slow progress, low efficiency (or quality) and a lot of time put in to continue the motivation. Though I learned great project management skills from going on that path trust me, you won't get usable work done in any great number.
Best,
Ruyei/Rob
P.S. Also don't be surprised if you get mostly paid responders...this is normal for posts such as yours with little information.