Welcome TBtest...or PPD for short...you folks in healthcare just got that joke.
Inside guarantee will get you a standard inside room. For your first cruise, don't expect them to bump you up much. They tend to be more accomodating the more you cruise with them! But in all honesty, an inside room is standard whether it's on Empress or Upper or Promenade.
LHP is right on target. Costa Maya is fairly much a waste! Belize is fun. If you like beer, take the Belikin Beer Tour. They tour you around town, tour the brewery, and then all the beer you can drink! Never been to Grand Cayman.
Gotta warn ya though...you just got bit by the cruise bug!