I'll default to a savvy local like @Remington Lyman to illuminate Ohio specifics, but in general I'd pay attention to the following on investment properties:Sewer line -- these are hidden and I want to make sure they are healthy OR I have a budget for replacement right awayHVAC - have the heating and air units been well maintained? 

I have made a great friend with the next door neighbor who always watches the property, and met another neighbor who does heating/cooling, and replaced the heating system in the house at a very fair price.

The pros with the duplex are you have 2 units with essentially one set of "cap ex" features like your roof, heating system, etc.

There is also a gas wall heater that provides 50,000 BTU, but I thought it would be nice to have a wall heater in each bedroom for supplemental heat. 

But then 2 minutes later I received a threatening email from Section 8 saying “I have been aware of the heating issue and understand that you have been working the issue with no resolution.

., no heat in the middle of winter). 

So they are going to do a heat treatment to kill even the dormant bugs hiding in the walls and such.* My question is: If we have a professional come out, and treat for bed bugs, would we then be free to rent out to tenants after waiting the two-week period recommended by the extermination company?

The wind getting into the crawl spaces and freezing the pipes if it's not properly heated can be costly. 

The issues they faced from bursting water lines, heating units failing, extreme wear/tear on roofs etc.  

If the basement is fully finished and a livable, heated and cooled space, with egress and minimum ceiling heights, it would be counted as part of total square footage of the house.