The Shearwater 39 is an excellent boat to be doing this in. Dudley Dix-designed and S.A.-built, which means it should be capable of taking the horrible wind-vs. current seas off the Cape of Good Hope without trouble.
Its bigger sister, the 45, has been for a number of years now on my short list of "boats I'd trade to if I won a lottery". The J/160 and the Saga 43 are also on that list. Despite the fact I've now got a sailer-motor in steel, I still really enjoy the idea of a perfomance cruiser.
Re: your trip. I wouldn't make any hard and fast plans about not going offshore, and if you have a Shearwater, why not consider a Virginia to Bermuda run and back for practice this summer (in between hurricanes...)?
You might find the Ditch in a Shearwater dirty, 90% motoring, and expensive, as well as stressful due to depth, nav and keeping a watch issues. Check the pilots for December/January...you may find it's a reach to broad reach until the Trades, and then a turn west/southwest down into the Caribbean. Two sets of reaches is a good, if rolly, way to shake down the crew.
Another option is to take an experienced crew (maybe a woman to avoid teenaged girl-burly young seaman interactions!). That way, you, the crew and one of the three remaining less-experienced crew could pull off five to ten days offshore passages without a huge amount of strain and keeping out a weather eye and a moving set of "outs" if something nasty comes in from Africa.
Just some thoughts...but I'll bet the ICW will be crowded with stinkpotters and weekenders heading south for Christmas/New Year's, and I for one would hate to be in a brackish traffic jam/serial bow sniff.