Florida Landlords: A/C: Is a wall unit with heat sufficient?

[Jonathan Cronkite]

Is it legal to only have a through-the-wall a/c unit WITH HEAT that is designed for 550 sf? 

I'm doing minor rehab to a 988 sf house that does not have central air/heat (location: east of Orlando, Merritt Island).  It just has 1 wall unit (which needs to be replaced).  I got quotes from 4-6k to install central air.  Of course, I'd rather not spend that kind of money.  

The new unit costs $550.

I was going to put a small window unit in each bedroom (w/o heat).  Good idea or waste of money?