Mollie, I would recommend contacting your local health department and find our what the laws are in your state/city/county. Google can go a long way too in finding out about if your state has a cottage food law and what the restrictions are.
I know you are anxious to get started, but don’t abandon the “business” part of “Cake Decorating Business”. It’s important to understand how your business will run. Business plans, costing out your goods, etc. are all important to know, especially if you are planning on giving up a “real” job to pursue your dream.
Good Luck!
Jenniffer White, Cup a Dee Cakes - http://cupadeecakes.blogspot.com