You also need to check with the utility companies and get cost estimates from them for availability, fees, hookup charges, transformer and power line/power pole locations or relocation requirements, water, sewer,gas, cable etcYou will need ball park cost estimates from site work contractors for site work, roads, installation of utility lines etc.Once you have some answers to these questions you can get estimates from site-work contractors to do the work.

That's simply too much work, gas money, and time for my liking.

I called the contractor and he said it is very ridiculous as the gas appliances are property vented to the exterior now without using the chimney and the chimney is no longer being used. 

Oil/Gas too.Medium income compared to what is for sale.

I would get estimates for utilities connections (gas, water, electric) and then, if it still makes sense, architect's plans made so you can  get building estimates so that you are good to go if AUDs are authorized.Do N-O-T build one without permits and permission.

In addition, Property Management, Utilities (Sewer, Water, Gas, Electric) if it can't be billed to the tenant.

All of the units will need extensive electrical, plumbing, sheetrock, fixtures, probably gas lines, some need masonry work, another has termite damage, two others have mold from failed siding, there is some roof repair to be done, tiling, basically everything.

She's invested a lot into keeping things up to date as far as the equipment and gas pumps etc go. 

New roofRestored exterior of the cabinRemodeled bathroomsNew appliancesNew granite countertopsBrought natural gas to the propertyInstalled Central HeatConverted spare space to a second rental unit!

(some not even window units)Heat could be supplied by electric or gas space heaters so central heat isn't required either.