We also have a bucket of "approved hanging devices", a small hammer and a picture measuring and leveling device that we loan them for one month.

Local (on device) storage that later syncs when web access is regained would be a slick solution.Robust backups - both online/continuous backup plus the ability to dump a snapshot of data to an external hard drive.Easy access via search to contact details.What deal(s) they're a candidate for.Ability to text through the app.When responding via email, text or phone, auto suggest a follow-up task with a drop down for when to make contact next.Calendar that syncs to your smart phone.Ability to schedule appointments with fields for location and notes for the meeting. 

I've heard there are sub-meter devices you can hook on to the cold water line coming into the apartment that can monitor that individual units usage.  

It can be accessed from the computer web browser for the best use, but it does have an app. for mobile devices.

It isn't dissimilar from taking a company public. 

I’m a 27 year old medical device sales rep who wants to build passive income and quick the 9-5 grind asap lol.

It is a simple device that measures motion, temperature, light, sound and humidity.

In most states, they’re actually required by law.If for some reason you find you don’t have these devices, and they’re not legally required, I’d still get them and install them as they’re just good safety measures/peace of mind. 

There are also heat tapes available to wrap pipes with and these can be plugged into a temperature sensitive device that only turns them on when the temperature is low.

If the building is older major items that might need repair or replacement is the roof, HVAC systems, outdoor lighting, back flow devices, private hydrants, any fire suppressions systems like sprinklers/risers, parking lot, marque signs, awnings/canopy/overhangs.