Mark,
I would listen very closely to @Brie Schmidt and @Jon Holdman
Trying not to make a mistake can all be overwhelming if you let it. At the end of the day you just have to pull the trigger.
I have been looking at the Gross Rent Multipliers (GRM) for only duplexes in Nashville-Davidson County dating back to March-2015. In nice areas the rent multiple is around 130-140. The highest I have seen is 160-180. In Antioch it has been running between 114-136. In Hermitage and Madison high 80's - 103. And everywhere in Nashville is generally over 100.
Those are market rates and I would be looking to be at the low end or below the market rate - as an investor. You have to be taking some risk to get a below market rate on most any piece of real estate. (In commercial real estate this is called a gross income multiplier (GIM) which is the inverse of a overall capitalization rate...anyway).
Here is how the GRM works. Lets say we have a duplex that rents for $500 a side ($1k per month gross) and it sold for $100,000. $100,000 / $1,000 = 100 GRM. Conversely, lets say you had a duplex that rents for $1,600 a month and everything was selling at 120 times rent, it would be worth $192,000 (or $1,600 month gross rents X 120 GRM = $192,000).
Deals are a matter of perception and what your individual goals are. And this is exactly what Brie was saying. People paying high GRMs are doing so in parts of Nashville where they anticipate the value of the property to appreciate organically creating equity for them or higher rents soon. And when people pay lower GRMs it is because they are getting better cash-on-cash returns like Jon was describing.
Start looking at these numbers in your area. I am not saying many buyers necessary consider this formula or this is the only thing to consider when purchasing a property - it is an appraisal tool, to be certain, and is one way to look at the market prices.
You should definitely be considering what Jon said. And he has some other post about it. The typical management cost in this area for something like this is 10% of gross rents per month and you need to include it in your expense calculations.
GRMs can help you gauge what is a deal and what isn't in a market. It can help you figure out what someone would pay you if you wanted to sell.
You can see how finding something with below market rents, where you can raise the rents, can raise the value of your property. So you are also looking for potential in an investment property.
Good Luck!