For context, it's a $700-800k 2-unit MF, which I'm indifferent about in terms of going the owner-occupied vs pure investment route.

This post is purely opinion based although I suppose some may have experience with this.

I’ve had this tenant that I already plan on not renewing with, but my city called today needing access to the building (4 unit) to turn off water.

This includes gas, electric, water, sewer, trash etc.

I would ask the owner for the age of the roof, age of utilities (water heater, boiler/oil tank), and ask if/when the most recent upgrades were made to the property.Of course, take the responses with a grain of salt.

Oil tank removal and remediation should be the seller's responsibility, not yours, UNLESS you're a very experienced investor getting a tremendous deal sold strictly "as is" where you've waived all your inspection rights.The worst case could be significant soil contamination requiring thousands of dollars in remediation, followed by soil and ground water tests by the state of NJ.

Not sure if watering helps or hurts, but your tenants are not going to water.Is everything separately metered?   

I then but a Tiny Home on it and set up my PV system and water catchment and lived there off the grid for 4 years.

The things that draw power are water heaters, and appliance.

Sorry, but I need to tell one more short story.I have a 24-unit apartment building and I had one tenant who had moisture on his windows every day where it looked like he sprayed the window with water from the inside.