Since the developed part of the property is basically a "Barn" with un-insulated walls and a roof I am assuming this portion should be minimal (The property is a tire shop with a small drive in portion non heated).

It is a bigger house but has no garage.Also its quite ugly.Square footage and features (number of beds/baths, finishes, heating style, etc.) definitely play into the home's value.

You need to include insurance.Are heat and HW electric or paid for as part of the HOA?

One idea is to add Gas direct wall furnace but not sure if it's enough to heat a 1,000 sq. ft. apartment.   

I personally agree that this is the way to go most of the time, especially with how heated most markets are these days. 

How are heat and hot water delivered to the apartments, @Lisa Brooks?

As demand heats up in the spring, driven by the growing number of millennials entering the market, the supply of homes for sale could hit its lowest in history.

Does anyone have experience with a coal heated rental property?

Go through the home and make a list of items that need to be fixed up (i.e. flooring, roof repair, heating and air conditioning, plumbing, etc).

Separate thermostatic control of heat. 24/7 access to breakers.