Skipper Bob has a book "Marinas on the Intracoastal Waterway" It includes information Marinas on Floridas West coast. The listings include marinas that except liveaboards, the costs and amenities. It includes most marinas. You can get info on purchasing a book at http:/skipperbob.home.att.net/
As far as the type of boat, a trawler would be my first choice for a liveaboard. It's just nicer living above the waterline and as it seems it is going to spend almost all of the time in the marina, fuel is not a problem.
They can charter a boat out of Regatta Point Marina in Palmetto and just not take it out. While all marinas are not alike this is a fairly nice one and it will give them a feel for marina life.