Is there a marina in AC where a boat can be moored to live aboard and sail? Are there boat brokers or sales on the island?

There are limited spaces. I have a small boat marina, but the draft is limited to about 3.5 feet, so unless your keel is retractable, forget it. The Yacht Club has larger mooring with utilities, but of course is pretty expensive. Most sailboats just anchor off-shore for their stay.