gregaro, Look at the top of each page there will a "Forums" button. When clicked it will open a large list of topics about diving, equipment, training, Where to go, almost everything that can be done underwater. You've already seen disagreement about camera brands. . . and we all have to promise to play nice here.
Scroll down the list under "Forums" till you find "Photography". . . Under that topic you will find nice places to play for the "Nikon" or "Canon" or "Olympus" kids. There are some nice children there that will answer your questions about any equipment. . . and there are those that don't play nice. Each person is giving you their opinions on the equipment they bought, and very few people can afford to buy one of everything to give a comprehensive answer. You can get started for a few hundred dollars, or pay $20,000 easily.
While in Cozumel, talk with some of the dive shops to try their diving services, and ask for their advise about renting camera equipment. There was a fantastic photo shop that gave lessons, and rented camera gear. . . but it closed and the people moved to Colorado. There probably will be equipment to rent from other shops.
Read the board even after you get down there. Visit with the local dive shops. And try different kinds of equipment, in the water, before you buy. Also, At the top of each page is a button for "Photo Gallery" find the kind of pictures you would like to take and look at the equipment used to make those pictures.
