I think this is a wonderful romantic thing to do. Give a call to CN and see what you need to do to set it up.
As to what to wear. There is no dock at CN so you will need to wade out in the water to get to the boat. So I would suggest your best swim wear for the evening.
I haven't personally done the trip, but I've heard that they do supply you with drinks and snacks and will take you out at sunset. How more romantic can you get?
Give CN a call and they will take care of everything.
Juliann & Jeff
Jamaica Soon Come