I started this a little bit late into the project, but I wanted to post the steps I took in finishing the project. Almost the entire thing was digital, save the line work and a bit of paint (as you can see in the first picture) and I think it turned out looking like I didn't do much digital work on it. Besides the kid in the background. He looks totally digital. But I'll work on it.
I scanned this first one in and made it a separate layer. I then made that layer "Multiply" and started painting underneath it, so it would still have the tooth and grain of the paper to it.