Let's take a look:
Once things are cleaned up and looking good, the next step is to set up the Layers panel for painting. I've tried tons of different ways to go about painting artwork in Photoshop, and the best technique that I've found is to isolate the black lines of your artwork on one layer, and set up a second layer for your color. To get yourself set up like this, double click on the Background layer and rename it "Artwork" or "Lineart." Next, create a new Layer for your color, and move it beneath your artwork layer. Finally, set the blending mode of your artwork layer to Multiply and lock it down.
Painting artwork in Photoshop is a lot of fun, and it's even more fun when you can speed things up and do it quickly. Here's a handful of techniques to help you along. First, grab your Brush tool from the toolbox by hitting the "B" key on your keyboard. Next, grab a color either from the Swatches panel, or by clicking on the Foreground or Background color swatches at the bottom of the Toolbox to use Photoshop's Color Picker to set a color.