I was just wondering if I want to do the beach if its better to book an excursion that goes to the beach or just find a beach ourselves
Depends on quite a few things; for the ports you listed, most of those things are: how comfortable are you finding your way around on your own? Safety isn't really an issue, but you'll have to find a cab [not that difficult] keep track of your own time [also not difficult], find a cab back [still, not difficult], but for some people it can be quite intimidating.
Google for your ports stops' beaches, find one or two that are popular enough to have cabs waiting [or callable] and that have your preferred level of clothing- some can be nude, especially on St Maarten.
SIG: If you're going to create the drama, at least supply the popcorn.