Columbus has the largest company in the state, Cardinal Health. 

., or Boston, Philadelphia offers relatively affordable rent, or section 8 tenants, especially those who are relocating from more expensive areas. 

Myrtle Beach area and clearwater florida are more affordable for what we are looking for. 

house hack in some sort of fashion.Either buy a duplex or large single family that you can rent out a room/side of the houseOr buy a fixer upper in the best neighborhood you can afford. 

Can you afford to have zero possibility of a tenant for those months that you don't have it listed?

You do not actually need any income if they have high enough income to afford their bills plus your new house.

Non-passive to achieve this level of return.Add the addition of the ADU makes the main unit rent controlled if over 15 years old.the work to add an ADU likely exceeds the effort of a brrrr that can achieve infinite return  Experienced investors are adding multiple ADUs by leveraging items like bonus density, committing units to affordable housing, etc.  

There is a growing trend of apartment owners investing in submetering systems for water as these have gotten more affordable.

Some are basically affordable housing and some are vacation type rentals.

Once the time is right, with enough research, I would jump into a market (hopefully local if affordable) and get started.