Last month my husband, daughter, and I chartered a 36 foot Jeanneau with Sunsail in the BVI. We had only been sailing for a little over one year. We took all the courses you mentioned and bought a small trailerable sailboat to practice on and give us confidence sailing. We also became members of Marina Sailing, which allowed us to rent boats in the size range of the boat we were going to charter. I would highly recommend doing that. Your lessons will start you out on small boats, and you will graduate to larger ones, but you won't be logging in very many hours with the lessons alone. Although being part of a Flotilla will be fun, it doesn't replace sailing experience, as Zanchin mentioned. The BVI is a good place for your first charter experience, and we had a great time, but there were some pretty scarry moments, especially with 6 foot northern swells and winds in excess of 30 knots. You will probably not experience that kind of weather, since you are going in July, but you may want to log in more sailing hours than just your lessons, so you can have fun and not stress. The good news is that with your extensive motorboat experience, you can always lower the sails and motor if things get tough.
We are doing a flotilla in the San Juans (Washington State) in May, because we like the idea of meeting other sailors and socializing, since we will be sailing alone. Not necessary, but should add to the enjoyment of the islands. I think you will have a terrific time!