Don’t listen to the b.s. U. S. propaganda. It has "never" been illegal for Americans to go to Cuba, and is unquestionably the safest country in the caribbean to travel in. But go now , they are on the brink of government change and this will be your last chance to see the Cuba of the Castro revolution. There are millionaires and billionaires lined up just waiting to pounce and it will change Cuba forever. returning Cuba to the playground of the affluent. It will become too expensive for the regular joe.
For now there are pristine reefs and coral walls unblemished because of the small number of divers. Stay away from the North (varedero etc) as March has windy conditions and rough seas.
Best accessible (shore) diving is on the south at the Bay of Pigs. Which have shore shops catering to divers.I take my own diving equipment but from what I have seen the rental stuff is top notch, unlike rocks tied to nets (for weights) as some would have you believe. Although some would have you believe they are ignorant third world extremists, the Cuban people are very friendly and happy. They boast the highest literacy rate in the world, and have extremely high education, safety and health care values and facilities.
Because of the lack of infrastructure there are thousands of sites just waiting to be explored, especially around the southern isles, if you can rent a boat.
Go for it............ Cuba is a divers paradise, hidden from ordinary Americans by self serving bureaucrats