What size boat would you need to run a Fishing charter for marlin, ahi, and the like?

I admit, I've only been fishing for those kind of fish a couple of times, all of my experience comes workin/fishing in AK, but I'm moving to a tropical area in about a year, and I'd like to set up shop there. Besides lures and poles and the basics, what kind of stuff will I need, and how big a boat (I know "people have chaught 700lb marlin from a rowboat!...and all of that crap, but I mean, to have 4 guests (my ideal #) a deckhan and myself, with room to hold the catch for a full day charter). When I Deck handed for a friend in Hawaii, he had a 42 foot hatteras that was awesome, but I could see getting by with less, at least to get started, but maybe that's how big you need...?