Passengers
Ballast must be as full as possible. After you launch, simply open the valve, when the air stops coming out from the vent, you are full. I suspect that as you add weight (bodies) and the boat rests lower in the water, you could add more ballast, but it is not necessary. As far as passengers are concerned, how many did you have in mind? I would suggest that you keep your sailing skills and that of your passengers in mind. Remember, as you sail, you will need room to change positions and trim the sails.