If you want to understand 5-year outlook, I'd look for multifamily construction data in your area to understand what level of new units is and will be coming online in the near future. 

Your main concern should be whether these bedrooms and bathrooms on the lower level are legal and have the proper egress require for fire code and livability.

dont over think this its not that complicated. important issues are.1. cost of capital2. knowing what a deal is or is not.3. good reno crew or contractor  4. good agent that will tell you straight what its worth when done and what level you should rehab to.5. a market that is actually moving napkin math works  trying to drill down to decimal points does not.

This is next level genius!

That’s a Cardone-level play—treat asset management as the CEO of your investment.

Bathrooms if you can zero threshold people love those and as they age out they need it anyway but that would be for main level. 

Example: owner bought $1 million SFH in San Francisco as primary, built 400 sq fit ADU, lives in ADU is making gross rental income STR  renting out two levels of main house, grosses $13,000 month.

Just make sure they are familiar with your state tax laws if you have state-level taxation.5.

Our family had a summer home that had an open metal roof over part of the patio, and when it rained everyone was uncomfortable with the noise level.

If, however, there are any gaps at all in any of the above items, even a gap so small a mouse can squeeze through, that tenant will exploit it and your life just became a 7th Level of Dante's Inferno.....:)