This, I'm afraid, is not the place to be looking. What you're asking, essentially, is "how do I go about designing and building my own 7,000 sq/ft house?" without any formal training. I'm not saying that you're dumb, and it sounds like you have some schooling or experience with ships - but yacht building is a far cry from being a hobby.I've been around ships of all kinds for 25 years and owned one kind or another for 17 years. I would start learning about structural engineering, marine engineering, naval arcitecture, welding, and carpentery. For the design phase, I recommend having someone draw up the plans for it. You tell them what you want and they'll tell you what you can do. Then run the plans by the Coast Guard. They're kinda like the cities' building inspector. They'll give you a thumbs up or thumbs down. But they will need to inspect the ship throughout its construction. I guess before you start anything, contact the coast guard.
www.uscg.mil