Tankless water heater question

I'm looking to buy in Florida. The house I'm looking at needs the water heater replaced. This is northern Florida.

From the research I've done online, it sounds like a tankless water heater would be more affordable than a typical tank design in the area.

Can you just swap a tank directly with a tankless, or is there more to it such as needing different piping sizes or power to the heater?