Well, for technique I think with your level of artistry you should be able to pull it off with enough shoe-reference research. I'd project an image on the van before tracing it just to be sure...but yea.
Since you've never done shoes before, I recommend you use simple erasable whiteboard markers to trace it first. If it looks fine, then paint it. Don't use markers for the final product, even good permanent markers will come off.
If you've ever had your car graffitied, you'll know spray paint is a bitch to buff out. I'd suggest using just that, and you might even add a waterproof layer of fixative on top of that to further weatherproof the art.
airbrushing would be awesome if you had access to airbrushes.
As for drying, dry it in a well-ventilated area. Build up layers of spraypaint instead of spraying them all on in one go. It will help the drying process as well as prevent unsightly paint running down. You can use a fan to speed up the process, but I doubt it'll help a lot. Spraypaint pretty much dries on contact already if you use it sparingly. Keep the masking tape for marking out the borders on though, just in case it runs when you leave it to dry.
oh and when you're done, PICS PLEASE!