I have security monitoring through a company  that uses the Qolsys IQ Panel in conjunction with Alarm.com, and this works as a Z-wave hub for multiple products including security, wifi thermostats, electronic locks, lights, smoke detectors, carbon monoxide, freeze detectors, and more in the future I'm sure.

When I charge $5 for a bulb or battery for a smoke detector don't complain.

(had to tighten a hand rail, replace the two pumps on the furnaces, put batteries in the fire detectors (I forced them to rewire the fan and lights in the bathroom).Its a pain dealing with an unmotivated seller, and a real estate agent that relies on email to get anything done (especially with the city (when repairs were done, told me that main inspector was sick, and underling was doing inspections and that he was emailing back and forth about getting the rein spection, It took one trip to the city hall in person for me to get the place inspected the next day)).None of this would of happened if I hadn't had the code to the lock box.

Same for smoke detector batteries.

Just fix the roof, give it a good cleaning with appliances off of Craigslist make sure plumbing, heating and cooling works and is safe to live in (no bare wires, black mold, smoke detectors etc..) when you are ready to sell it than that's when you would want to upgrade it.Good luck Wishing you success;) 

I encourage you to do the research yourself but from the what I remember reading, HUD says the only thing that needs to be changed is the drywall and the smoke detectors.

They did not install any carbon or smoke detectors. 

My current home wouldnt pass the current code ( no house wrap , not enough insulation in the ceiling , walls now have to be 2 by 6 ,  dryer has to be 4 wire , not 3 wire , smoke detectors have to be hard wired ,  fire sprinklers)   I dont have to change a thing , if I did it would be a small fortune . 

Lawn, bark dust, trim shrubs, wash windows.Paint interior.New flooring.Do heavy cleaning to tub, sinks, faucets and appliances early to evaluate whether they need to be replaced.Other cleaning, repairs, and replacements.Install smoke detectors & CO2 detectorsPrior to placing ads, the following needs to be decided/ready: estimated unit availability date, how to handle utilities, market rent amount, deposit amount, any updates to application, policies, or screening process.

i would put in smoke detectors, handrails and lighting, i also believe that because it is a multifamily that is a requirement that even the town has. if you are referring to electrical outlets and separating circuits, then yes, when you remodel that triggers bringing everything up to code.