Thanks for sharing your ideas. Where we live, near Winnipeg, Manitoba, Canada, we are very close to beaches (freshwater, not salt water). We aren't beach people and usually like to have a plan.
Snorkling here just doesn't happen as there is really nothing to see and the water is quite murky.
My preferences are to be in the water at each port and will try to do that. We have never felt that the water was too cold, though I am sure it varies somewhat from port to port.
We are thinking of a private tour guide in Roatan but the other ports through Carnival.
We enjoy the time spent planning our trip, so we will keep looking at what to do!