If you have a Belizean passport you won't need a work permit. As far as a business license, on Caye Caulker you don't necessarily need one to open up, but if you want to offer credit card processing, or get a liquor license, you will need to register your business in Belmopan at the business name registry. Its a smart thing to do anyways, that way no one else in Belize can use your name.