Advice from an expat
Living aboard most likely impossible here.
Although I don't share in the opinion that it would be dangerous, or even risky, the problem is the one yacht club, in Puntarenus, is defiantly not live-aboard friendly. I have my Boat docked in San Diego because you have to be a resident to get a slip for more then a week or to, and then you would have to pay the outrageous import tax up to 100%.
that being said i did look around abit and found a marina in golfito
called bannana bay, just google costa rica marinas
i believe they allow live aboards, though golfito is way way out of the way.
i have no idea if the Caribbean side has anything to offer, but i would imagine some where around limon such a marina would exist