My first question would be: Do you have a Near Coastal OUPV Captain's License and are you carrying business liability for the business. You may already have these items covered...but I would ask unless it was in your business advertisement.
Have no idea what you should charge...normally this is based on the norm for a guided trip in that area...but kind of hard to compare sitting in a Kayak on the Gulf of Mexico to being in a charter boat. Are there any other folks doing this type charter there?