There's an active sailing scene in Florida. It should not be difficult to get experience anywhere in southern Florida. Tampa, St Petersburg, Forth Lauderdale, Miami etc. Crossing oceans is not so difficult, but knowing what to do when things fly to s**t, is vital. This is particularly important on the route you are considering between Florida and South Africa. Unless you are going around 'the back way', you're going 'uphill', for 8000 miles, all the way.
Try to make contact with local sailing clubs and, if you are a good learner, can take direction, and have plenty of logic on tap, you will have little trouble in grabbing a spot for mid-week and weekend racing.
Best of luck. Hope you get to Cape Town.
"if at first you don't succeed....Redefine success"!