Does anyone have experience with ADU's (accessory dwelling units) in any market, but particularly Cincinnati?

Study the market.

Here’s our OPINION for the Metro Detroit market (use as a template for your target area!)

Since the house is for sale, the most important concern is marketability.

However, on the renting side, we have seen an increase in inventory of days on market too. 

I am working with some NJ clients on turnkey investments in the Midwest/midsouth markets currently.

That would be your downpayment and or market value the day you buy.  

I am proficient in investing and confident in earning 7-10% returns in the market over the next decade or two.

Here is a list of why adding a single ADU in single family zoned areas in my CA market is typically a poor RE investment:1) The value added by the ADU addition is often significantly less than the cost of adding the ADU.

we build at or slightly below the average new build in our market where there is high absorbtion