Do I need to lay down any kind of moisture barrier if these are laid on concrete? I know concrete can sometimes release moisture and wasn't sure if there'd be any issues with this getting trapped underneath in Florida.

To test to see if moisture is coming up through concrete, you can tape a sheet of plastic over the concrete and leave it there for 24 hours. If there is condensation on the plastic when you peel it up, you need a moisture barrier. Once you have considered your climate and materials, you can decide if you need a vapor barrier for your floors.