I live in the main level unit which has Central AC/Forced Air heat.

I don't think adding another element to the arrangement that could potentially cause disputes is smart and I haven't had anyone abuse the heat/AC over the several years I've done this so I plan to keep it that way. 

The house had central heating but not AC.  

Having access to the MLS, running comps and understanding the Miami market will give you an upper hand. 

Current new tenants have a dog that they chain outside, in the worst damaged area, and in the heat, which I have given up on trying to repair, and when they move I will install a nice stone arrangement, perhaps with a small crabapple.

Are they split or does landlord pay water or heat (gas or electric)? 

I agree about the heat of the current market.

There was no heating or cooling of any kind.

I purchased a property in Miami Dade a few years back.

Some people will live in a place with leaking roofs, no heat, leaking plumbing, etc.