I repainted a gas tank with cans once. I think it looked pretty good. Ended up using I think 2 cans for it. Plus probably four cans of clear coat.
The biggest problem, if I remember correctly, is getting the right kind of paint. The whole laquer, enamel confusion. I couldn't get a clear coat and color that went together. I sold the bike so I don't know how the paint job endured time.
You probably will have a hard time finding flat black paint in a can that is appropriate and a matching flat black clear coat.
My best advice, if you go ahead with it, is to make sure you do several light coats. Nothing is worse than getting a run or orange peal. You pretty much will have to start over after that.
I'm sure someone will chime in with better knowledge than me. I want to know the same things, but I own a compressor so I will probably buy a gun and do it a little closer to the right way.