But there are these massive space heaters inside each unit that I think do use up a lot of energy so maybe I’ll look into an alternative heat source.

The air handler coils should stay clean from regular changing of the filter.

The only downfall is that heat/hot water is included but there were brand new systems installed in the past 2 years so they are pretty efficient.

If the roof or the heating system needs repair you will have $0 cashflow for awhile.

I raised their rent $100/150 but it worked for me as well because those tenants were paying their own heat over the winter and we won't get to their apartments till late spring.Tenant with lease moved out on his own.

Factor in your local PM commissions into that potential gross rents (40k- commissions) you are now down to about 30k.. minus maintenance repairs, late night service when the heat or AC goes out..

You will be paying for electric, water, heating fuel, sewer, trash given you are renting rooms of a SFH. 

Most of the main systems in the home are relatively new (hot water heater- 3 yo, HVAC/ heat pump 1.5 yo, roof 5 yo, new toilets, new garbage disposal), and the house is 33 yo.

I would like to make sure that once she leaves, the heat does not get turned off and the pipes freeze.

You get used to the heat, and yes it us different than CA.