Whether in Florida or NJ, if it is 90 degrees outside and well up near or past 75 percent humidity and the emgine just got shut off....even 16K for a main salon full of windows isn't necessarily enough.'
Yes, by the time the engine cools and the sun gets lower....you can chill meat.....but in the meantime....do you want an AC that can do the job?...or have one working overtime just to keep up with being comfy?
Most people do not realize the home sized air conditioner for a nominal bedroom cant be compared to a marine equivalent. Lots of reasons such as air transfer, insulation, windows per cubic foot, etc...etc....
This! ^^
Unless you're one of those tough-as-nails types who never needs air conditioning, when you need it, you REALLY need it. Don't design for the minimum, design for those hot days. We endured a 3-day heat wave in Eastport, Maine (where even homes and businesses have no air conditioning) and were thankful to find a dock close enough to an outlet that we could run a long extension cord to our shorepower cord to run the AC.
I strongly recommend two 16K systems. You can cool the whole boat using one if it's not too warm, or if you can only scrounge enough power to run one, or if one fails.
The rest of the time, run whichever or both, based on which spaces you're using, or not using.
Carefully consider ducting options. With my boat, each unit blows into it's own cabin, as well as into the saloon. I can close off vents, but usually the balance seems about right.
Another big decision is where to put the thermostats. You don't want them in a "dead" spot with no air movement, a hot spot or a cool spot. Ideal would be some sort of remote you could put wherever you need it, but I haven't seen those for marine units. You can always put off the decision, and try out different locations over the season before permanently mounting it.