So I'm unclear on what labeling needs to be for cake/cupcakes. I am a at home baker and working on getting kitchen certified (in Massachusetts) and I plan to sell cupcakes by the dozen in bakery boxes. Does this mean I need labels with all the ingredients listed?!

Good luck in your new venture! As a home processor, your best source for answers is always the licensing agency (and your home inspector, if already assigned). Forum boards, such as CakeCentral, can be helpful. But responses come from a wide group of individuals who may or may not be qualified to answer. You can start with this link from the MA Department of Public Health. However, it covers all food establishments and is not an easy read.