You can learn through trial and error. 

It sounds like the other additional issies related to the existing structure would also require some significant work for remediation, so there is definitely more to be analized in terms of the existing structure.In regards to wrecking the existing structure and building new, that would definitely be the easiest thing in terms of a Code Compliance perspective; however, I assume the financial portion of a project of that scale would be significantly more than any renovation work you want to do the existing structure.In terms of trying to add a 2-story addition onto the existing coach house structure(or any type of addition), this would Not be permitted without obtaining significant Zoning Variations (which have no guarantee of approval).

Additionally, rental costs across the state show significant variation, highlighting the diverse living costs within Ohio.

There’s lots of trial and error involved and your first rental property will likely not be your best.

The buyer can walk away with simply losing his option fee or he can choose to exercise the option.Options are like Ice Cream, there are at least 37 variations.

I am assuming the zoning variation was for a detached garage.  

Balloon" framing (1920's I believe).Radon.Plaster and lathe instead of sheet rock (pre 1950's) or plaster and wire mesh variations (50's) more solid than sheetrock but a real b*tch to repair or demo if you're remodeling.You've got Galvy plumbing but also need to look out for other kinds of outdated plumbing like clay sewer lines (pre-1930's, prone to collapsing, bellies, root intrusion), cast iron (1950's, often rusted and/or cracked by now), and PB (polybutylene, gray-colored water pipes, 1980's, prone to rapid degradation and subsequent bursting, mostly gone by now).Buried Oil Tanks-- Do you have those there?

https://strhub.co/ is a good site with a calculator, not sure if you can do a free trial on there but I've used it before!

This might be a good place for trial guests until you go live, but you only renting to them is a mistake unless you are not in it for the cash flow and this is truly just a second home that you don't need to make income on. 

If you’ve interviewed people then I’d suggest you pick one of them and do a trial run with this year’s set of taxes.