A) The economy heated up substantially with a lot of economic growth, If that happened your rents should go up as well.

Patrick's day is pretty much dead, then it starts heating up in April...

Tenant texted me this morning that the central heat wasn't working.  

Where's your heating source?

While water/sewer is easy to deal with, anytime you are paying for heat you are looking for trouble.

This was done more for heating efficiency purposes but it certainly helps keep any moisture from finding its way inside, although there wasn't much left after we did steps 1, 2 and 3. 

Once I have heat I can figure out just how bad the plumbing is.

You "got away" with it (so far) because of your income's ability to ride out the storm, but I do sense that you believe you will still be able to ride out any future storm too, even after buying (at a TOP price, in a heated market) your next "big house, with the wrap around porch"!

part of your responsibility is at move in to show them how things work,, how to turn on the heat, how the smoke detector works, how to provided a toilet plunger with the apartment so if they have a minor toilet clog they can fit it themselves,, and show how to use it, where the electrical panel is an how to reset a breaker,.... the stuff ordinary people would understand but renters aren't always ordinary people.Get a system for contact for repair requests,, have them text or leave on voice mail ,, don't go and answer each call right off the bat,, give a thought... call back and try and trouble shoot with them over the phone... as for toilet and drain clogs I'd let them know if plumber comes out for service if it is found that clog is from food, toys in toilet,, or grease they will be charged a service call. some use a form for this at move in. 

So, in reality, you're going to have to put in 1/4 of certain expenses, like utilities, on the back end of these analyses (Uncle Sam wouldn't like it if you tried to expense all of the utilities to the other 3 units and get your own personal heat and electricity as a tax-deductible expense anyway...).