Stevie:
Spray...That is a hard question at least for me to attempt to answer but I will do what I can. If I am talking above your head, please let me know.
I am assuming since you have modeled you have an idea on how to export a image with the flatten out polys in order for you to bring into your paint application. There is a (in photoshop) a spray brush you can use. If you have ever been to an art store, you will see racks and racks of paint brushes. Each brush does something different (size, shape, how much paint it can hold, etc) so what you can do is either create your own brush, purchase brushes from 3rd party vendors, or use the built in ones. I have found out (ad photoshop) that the built in brushes suit me quite well. Take a quick look in the help on how to design/use custom brushes.
Most of the effects achieved to clothing is either rendered images (using your modeling program, use the cloth modifier and make a plane that wraps around your model, with lighting effects) or hand drawn. You need to learn "shading" to make some really nice artwork. Shading and Highlighting is the best thing I can tell you besides using custom brushes (like the Chain Mail brush).
I hope this helps you in some small way.
Simpson
-This...is my boomstick!