"I want to turn my layer cake into cupcakes. How many will I get and what do I need to do?"
You will likely get 24-30 cupcakes. Start by lining the cups in a muffin pan with paper cup or coating the pan cups directly with nonstick spray or butter and flour. Fill each cup 1/2- 3/4 of the way. Most cupcakes take about 15-20 minutes to bake–test for doneness by inserting a toothpick in the center. It should come out clean. Cool the cupcakes first in the pan for about 5 minutes, then on a wire rack until they are completely cool.