The Miami boat show is coming soon. I suggest spending several days looking at boats there and looking at boat operators training schools. The typical captains course wont teach you how to operate the boat. You need a lot of time underway for that.
If I understand correctly you have little experience in boats. If true you wont be able to get insurance unless you have licensed captain operating the boat.
Be very careful in buying a used boat because inexperienced people often get something unsuitable. A full survey is a must.
I hope that you have more experience than it sounds because what you want to do is not difficult with experience it is very difficult withour experience. Boats and their operation is complicated.