Hey Scuba Girl good choice if you will be doing a lot of diving.
If you are not a total newbie ask about "La Parguera" on the south-side of Saona island and by all means try to get to CataliNITA island not to be confused with isla Catalina, Catalinita is on the North-East end of Saona island it is on the Mona Passage side of the barrier reef that goes North-South along the Eastern end of mainland DR, so the Eastern end of Catalinita is very close to very deep water and this is the best place to see bigger animals. Everytime I go to this site I see sharks, barricuda large rays and large schools of jacks.. Enjoy