How do I change cake recipes for cupcakes?
I've not yet found a cake recipe which I could not use for cupcakes instead.  
I always change the baking time and only the baking time.  I rotate the tray of cuppies after about 7 minutes, and after another 7 minutes or so I use the "clean toothpick" method to see when they are done.  
It does vary greatly, but from most cake recipes, I expect to get 18-24 regular cupcakes, about 40 mini-cupcakes, or 9-12 large ("Texas") cupcakes.