I'm not a pro but I have experience in comics, a pro comic artist would earn 200.00 and up for just pencils, guys like Jim Lee, Adam Hughes, etc.

From what you wrote, it doesn't sound like traditional comic pages, just panels. Maybe it's for a webcomic?

As for pay rates, you should charge whatever you feel is comfortable to do the work, don't pull out some random number. Figure out the cost of materials + your time.

Doing character designs is a big job, If it were me I would charge 250.00 per character style guide, but I would also retain rights to it's creation for the minimum of credit, maximum royalties.

But yeah, you have to watch out for scammers too, I've run into my fair share. Having a contract doesn't really help if you can never get in contact or know where this person lives, etc. I'd recommend only working with people you meet in person, or if they are serious they will pay you half up front and the rest on completion of the project.