I'd recommend a good underwater detector like an Excalibur. Give it a weeks' workout on the beach untill you get used to it and then take it underwater with you. If you buy a good used one and then decide you don't like detecting, you can resell it without losing much if any money. You'll need to research the areas offshore where you want to hunt. Most of the known wrecks and treasure areas are claimed so you'll either need to get written permission from the one with the rights or hunt unknown areas.
I'd start by going through the shipwrecks forum on this site and talking with those that have done what you plan to do. Maybe you can find someone to partner up with. Let us know how you do!