Small cats, say sub 40ft, are often seen motorsailing in typical inter island passages. Why cos they seem to get slowed or stopped by the wave patterns. AKA the Caribbean 2 step.
I think you should look for a cat with a waterline length of at least 44 ft. Check out the French islands for ex charter cats at reasonable prices. Something like this CLICKY
I am retired in the area you talk about as liveaboard on a monohull. If I wanted to house the numbers you talk about then a cat would have been my choice.
Re engine hours 5000 -6000 hrs is the approximate equivelent of 250,000 road miles. I would not be too frightened of high hours if the engines start easliy and don't smoke under load.