Verifying if smoke detectors are functioning, appliances are running and water pipes are not leaking is a plus.

I own a condo in Gatlinburg- 2/2 and the HOA is $290/mo but includes wifi, water, cable, trash, and sewer.

However, many rent supply stores have them for rent and every insurance claim with odor issues (fires and water issues (mold)) includes there use in the remediation. 

@Bill Brandt, that is just an estimate for Electric, Water, Sewer, and Gas for THREE units.

I would assume you would want to budget for roof 25 year life span, hvac 20 year life span, appliances and hot water heater 12 year life span, bath and kitchen remodel 15-20 year life span, etc.

With your current estimates, you're essentially assuming infinite lifespans for the property's various components (roof, foundation, HVAC, electrical, plumbing, water heater, etc.). 

I would bump your expenses to atleast 800/ month between 2 units of utilities and averaged maintenance and vacancy over the long haul as future gas prices, water charges, and maintenance could go higher. 

Any other expenses that landlord normally pays in duplex in your area like water/sewer/garbage, is snow and mow completed by tenants?

Another incident I had a tenant wanting me to pay her water bill after it was not repaired for two months.

The cabinets, flooring, and paint look to be in good shape from the photos, but what about the roof, foundation, HVAC, water heater, etc.?