If you're going to be their guide for dives, then you probably want at least a Divemaster (or other "Professional") certification. Whether you disclaim it or not, charging people money to go out on your boat and then you guide them on dives means you are going to be open to lawsuits claiming you were taking payment to guide them on dives and thus were holding yourself out as a scuba professional. It seems to me that it would be a good idea if you actually were - and hold the appropriate dive professional liability insurance.
But, second, what are you going to do with your boat if you are leading dives? Leave it unmanned and hope it's still there when you get back? Leave it manned by a crew member who is not a licensed boat captain? There was a recent thread about a boat captain and his mate getting out to snorkel while all his passengers were diving and the boat was at anchor. There didn't seem to be a consensus that the boat captain was breaking any laws. But, there was definitely consensus that it wasn't a good idea.
So, if you're going to own the boat and be the captain, and you want to offer a dive guide service, you might want to plan on finding one or more scuba professionals to work for you, so you can man the boat while your customers are diving with a guide.
