The idea here is that sizing a unit too large can cool the room before it removes all the moisture.

In a well-made house or building, practically, this doesn't matter a whole lot. No one will notice their humidity is high when it is 85 outside versus 95 (I'm using Freedom units since you said Florida). But at the fringes it might be noticeable (during a party with lots of people in spring maybe, or cooking a lot).

Now, this isn't really humidity control. It's just removing moisture from the air. Put simply, expect your output air (let's say 55 degrees) to be at fully saturated moisture content, 100% relative humidity ("RH"). This is because you can't remove more moisture than you cooled the air to, and it will pass over wet coils. 55 degrees at 100% RH turns into 75 degrees at 50% RH, about where people are comfortable. You can see this on a psychrometric chart or calculator.

There are simpler load calcs (Manual J) or the real-deal calcs using the ASHRAE Fundamentals handbook. I doubt anyone uses full ASHRAE for 6 total tons these days, Manual J seems good enough, though it's intended for homes. These will ensure your building is cool enough on the design day, meaning about as hot as it gets where you are. If you put in units that large, normal usage in the American South proves that humidity control will be fine. Note that commercial usage normally includes requirements for positive pressurization and some amount of outside air that is seldom done in home use, though if you're rich you might have that in your house.

The best humidity coutrol is via variable-speed units that run continuously by slowing down the fan and compressor. This is also more efficient because affinity laws tell us that the compressor power is a function of its speed cubed, while refrigeration is a function of its speed. It also ensures we are always moving enough air to get good de-humidification.

Note that this is just humidity (latent heat in the trade) removal, it isn't really control, per se, as we said earlier. That would require systems not normally seen for cooling outside of industrial rooms with very specific conditions, like high tech fab or testing rooms. What you might normally see is a humidifier to add some level of moisture in the winter or in desert environments. Humidifiers ar enice in the winter, but they are a maintenance nightmare in my experience, though I admit my experience is now a bit dated.

So, do the load calcs and figure out how many tons you need. Then see if you can afford the fancy inverter-based units that save you money in the off-season and keep air flowing all the time.

Continuous AC operation improves humidity removal efficiency. Fixed-capacity units short-cycle, leaving moisture behind. Inverter heat pumps run continuously at variable speed. Measure your facility’s temperature and humidity over several days. Log door openings to see humidity spikes. Calculate peak sensible and latent loads using your BTU spreadsheet. Select inverter units slightly above calculated peak load. Multiple smaller cassettes improve airflow and control near doors. Validate by running units and logging RH and temperature. Adjust size if targets aren’t met. Focus on latent load first; temperature follows. Avoid oversized fixed-capacity units—they cycle too much.