We then bought a property that had two 10,000 sf storefront office space buildings which are separately metered for electricity but share water/sewer.

If any of the electrical fixtures are already missing - like a ceiling light or porch light - sometimes you can see if it has copper wiring (good) or aluminum wiring (bad). 

The property has all new electric and plumbing pretty much throughout, with only the heat being on the older side.

we won't tackle carpeting. maybe if things were slower i'd give it a shot but for me, it's easier to pay for it and have it done in a day. we do all the painting, plumbing, and electrical work and more. we just finished roofing two separate garage bays consisting of 12 garages with metal roofing. it was fun!

Water & electricity?

Fiberglass insulation absolutely has to go in tight with no gaps, meaning cuts around electrical boxes, wiring, ducting, etc.

Try to keep the framing where it makes sense, any plumbing and electrical, and it should be well worth the money to finish it.

Electricity. 

Around here landlords usually pay for trash pickup, and communal electric (hall and exterior lighting).  

As far as I have gathered so far, I have 3 options, but am leaning toward the first 2 more strongly: 1) gas space heater2) electric heat 3) baseboards w/ boiler in basement.