Coz is one of the "must dives" of the Carribean, the others being Cayman, Bonaire and Roatan.
Where you booked will decide what dive op you are using, most boats are 6 paks and the DM will decide where you are diving based on weather and experience level. If you are with a big group divide up by experience levels or your dives will all be based on the worst diver on the boat! Your first dive will be some over dove site until the DM is sure you are not going to crash into his most beautiful dive site. Later if you are good the DM may ask for suggestions but other than some having swim thru’s they are all good.
Is where you are staying and all inclusive? Other than when we rented a home we always went with the AI and ate breakfast and lunch at the resort so as to not miss any dive boats then diner out unless we were doing a night dive. In town there is a ton of choices, ask your DM where the locals eat for the best food :) Avoid the tourist trap with the caged animals! The local food is Mayan, not Mexican!
The Taxi fare is for the taxi, not per head so if the driver says $5 don’t times it by the number of divers you stuff in the cab. Ask the resort what events are going on in the plaza, i’ve seen great car shows, craft shows and music events there.