I had a few companies come by and give me quotes on insulating, drywalling, and painting.

Depends on the insulation, size of the house, how you set the thermostat.

Currently, I have a few smaller projects on a couple of houses: carpeting/tiling floors, painting walls that contain LED paint, installing A/C and heating system, installing light fixtures, installing appliances, making sure electrical wiring is safe, installing recessed lighting, insulating/waterproofing medium size room in the basement.

Need to make sure insulation is solid in attic, and your CFM and btu/hr is high enough to handle the head pressure it has to supply to push that air up that much vertically. 

There is no insulation between properties in these old buildings.

I have seen people miss many obvious things (drywall, insulation, HVAC, etc) and they were costly lessons.  

The tenants pay for the oil, and I give a bit of a rebate back to them on the cost as I do know its a bIt more expensive - though some of that could also have to do with a poorly insulated house.

They then went to REI to sort out multiple assets into separate compartments that are isolated and insulated from one another. 

I'm approaching this whole project as a big learning opportunity, to develop a skill-set I can use for future projects.I have a lot of fun plans for the garage of this property, which is huge, insulated, and has a bonus room, as well as a good structure for a garage-top deck. 

We've been working with Merrimack Savings Bank because we participated in the NH Energy Program and got an insulation grant from the state that MSB sponsors.