The units had combo central air & heating which is not common in this class of rental. 

Our initial intention was to live there for years and slowly fix it up, as it needs quite a bit of work; think central heat and air, windows, fencing, as well as updates (among other things).

@Paul Hamilton based on my calculations and conservative round numbers I come up with ~$360 monthly cash flow with 5% down and 4.5% interest 30y fixed, assuming water/heat/electricty is billed separately.

Knob & Tube wiring3. home systems not updated (roof, plumbing, heating, electric)4.

Heat tape would be the best option.

@Melissa Hall asbestos is a possible issue with any heating system that is older. 

For example, HUD requires each room to have heat.

These homes (entire neighborhoods) were built in the late 1970s with 200 Amp service, heated only with electric baseboards. 

They notified me that also the thermostat is broken and they aren't able to set it to a reasonable temperature, this is not good since as the landlord I need to keep the heat at a certain temperature (Right now in Maine temps are in single digits).

I grew up in Alaska and I never used them all that much, but I also know Alaska gets some occasional heat waves in the summer.