Honestly if they need to store a couple suitcases I wouldn't mind, but it's easier to start strict and go more lenient afterward then the other way around.The second is most tenants are not careful about things in the attic like A/C duct-work and will lay or drop stuff on them causing damage and possibly extra wear on the unit since it is now cooling the attic instead of the living space or has restricted flow.

The main difference was installing a second gas furnace and separating all the duct work.

You can add the ductwork, or closet, or wall off a door to get the sf (and value) added to the house.

Smoke remediation requires cleaning not only the surface smoke, but also all that permeates into the HVAC system, ductwork, crevices, openings from electrical and plumbing, ventilation units, light fixtures, appliances, cabinetry, countertops, carpeting, carpet pads, walls, and woodwork.

It's sprayed on the walls and floors, but the biggest concern to me is the ductwork. 

Guess where all the plumbing and the electrical and the ductwork was?

Follow the gas line from your meter if its in basement and see which furnace it goes to could go to both but its doubtful.I have ran across ductwork that a clown didn't install right and someone was getting free heat and air in a bedroom and bath.

I would imagine, given the building's age, that it would need to have the duct work put in to accomplish this, which would have a steep price tag.  

On another note, as FYI, the coffered ceiling is likely a capitalized consequence of creating the open floor plan and adding central HVAC... concealing a dropped beam(s) perhaps, to create the openness, and at least in the Kitchen area, it is concealing ductwork.  

If you have duct work, make sure the ducts are clean and the air registers are not blocked.