Yes, the Sandals resort is nice, you shouldn't have any issues with that. The reason you are reading to stick with a ship's excursion is that you are safer that way. But that is true for any port for a first timer. With a ship sponsored excursion, they will get you back to the ship on time. Unless you are a comfortable traveler and are okay with exploring on your own, stick with the ship's tours the first time until you know how cruising works.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013