I don't want to disappoint you, but we went to several "botanical garden" type places while we were touring around Ochos Rios and I never saw a whole lot of really pretty tropical flowers. And Tai Flora there told me that most flowers have to imported, which is why they are so expensive. So if you are really picky about the flowers you might be a bit disappointed... but if you are open minded I think you would be fine.
Also, do you or anyone in your wedding party have any experience with flower arranging? Cuz it's harder than it looks! And you will need some supplies, like floral tape, pins, ribbon, etc. I'm sure you can get all this once you get there, you just need to know what to look for.