well as am artist who does comics for others I can tell you that a writer is expected to have there story blocked out and completely written. you will also need to know exactly what you want and when you want it.
most comic book artists get payed per page on a averaged of 55$ a page.
to hire a artist you have to both agree on the terms of a contract. then you both sign it.
I myself am a freelancer and we have sites you can go to. most of us have our own sites.
theinkcat.com
this is mine for example.