You''re asking a lot of questions, and many of them each have many answers...which in fact is the fun of living on and cruising a sailboat, IMO.
Truth be told, you don''t know how much ''boat'' you need yet...nor do any of us. But it''s hard to be sure about size (and need I add, the notion of living aboard a boat at all!) without some first-hand experience. A chicken-egg dilemma, as it were.
I''d encourage you to take a couple of initial steps. If they seem costly, think of how much money you''d otherwise commit while knowing less about what you are doing. If they seem to take precious time, imagine how much of your time will be claimed by a boat once you choose it. These are basic steps many of us have taken, each of which should help you develop YOUR OWN answers to your questions:
1. Begin some thoughtful, disciplined research. Pick a couple of broad references (Trish''s rec of Voyaging Handbook by Beth Leonard is one excellent one IMO, Calder''s Cruising Handbook is another), take it slow (you''ll find LOTS of areas where your knowledge may be skin-deep initially), and digest what you read.
2. Join SSCA (www.ssca.org) but also purchase their SSCA Bulletins on CD; you''ll get 7 years of monthly bulletins, easily sorted and searched, which will bring you aboard many other cruising boats to hear their views on an infinite number of issues.
3. Sail. Sign up as crew for beer can races; beg yourself aboard for daysails in exchange for maintenance work; walk boatyards to find opportunities aboard boats once they''re launched; use local rags'' "Crew Wanted" ads. One hour on the water with knowledgeable others = 10 hours in the books.
4. Bareboat (if you have friends who can do the skippering) or charter with captain one or two of your ''finalist'' boats, in waters that beckon to you - that way, you''ll be trialing both the cruising area and the boat. As one example, we scrounged up for our first exposure to sailing offshore a local Cal 34 in the harbor, gathered friends together to help spread the cost and increase the fun, and we sailed over to one of the Channel Is. off the California coast for a weekend. Cost = minimal. Value = Immesasureable.
5. If possible, before buying the boat you think you want, sail on it for an overnight with the owner. If not possible, consider daysailing a similar type/size/brand from a rental firm. Expensive? Rather have the money to pay a surveyor or fund the haulout? Just reflect on how much, per day of ownership, you''d be spending to confirm your impressions.
Good luck. The cruising goals you mention - down to and perhaps across the Caribbean - can be done on almost any boat, provided its properly equipped with the basics and thoughtfully crewed & navigated. This means you can realize your dream without having to find the exact, right, perfect, etc. boat for you. Good luck!