Have only been diving east coast out of Fajardo and it was nothing special. Didn't get as far out as Calebra Island. The DM of the op (Sea Ventures) we dove with said there was good diving on the Southeast side of island, which is where we stayed, but there weren't enough people during the week for them to go out from there (although they advertised that they did) and there was no other op in the area (we stayed right by the marina.) Have read here on SB that there is good diving on the Southwest coast in La Parguera area.
Have only read about Mona Island and that there is not a day trip from the main island since it is like a 6 hour boat ride. Not sure if there are flights. Would have to plan a side trip there and stay a night or two.
Puerto Rico is a great place, IMO: tropical beaches/weather, great food, sightseeing, and pretty easy driving once you get out of San Juan. In San Juan to about 15 miles outside the city, morning and evening rush hours are crazy! We stayed in Palmas del Mar in Humacao and driving to other small towns was pretty easy. We stayed mainly on the east side of island as it is a couple of hours drive to the west side.
You're on the right track though if you're emailing dive ops. Hopefully they can be helpful with more info.