I’d like to buy a duplex in Florida with a pool. Rent units out but perhaps build an accessory dwelling unit on site so that I could visit sometimes as a vacation. (I live in the northeast)
You need to check the local zoning ordinance. I can't speak for Florida, but I would expect not. ADU are typically only permitted with Single Family Residence Lots. I would start with looking at the local zoning code
You need to understand the Florida ADU regulations. (And local City regulations). I don't know how it works there but in California you can put ADU's on Single and Multifamily zoned lots. In fact Multifamily zoned lots allow two detached ADU's.