And the second floor will not be conducive for patients unless there is an elevator, and ADA requirements.From both an beauty point of view and a  business point of view, and my personal experience I'm not much in favor of duplex conversions. 

This will give you easy and concrete data to work with.

***The buildings there for apartments seem to be mostly solid concrete construction with stucco walls, etc.

It's a concrete block single family house built in 1960, with 3 bedrooms/1.5 baths.

These buildings are cheaply built (stick frame, not concrete, you can hear your neighbors doing everything) but look nice to the average renter thats forking over $1,800+ a month for a 1br apartment.

Numbers matter the most, but 1) look at your exit strategy if you need to do so down the road. 2) Get your rehab costs written down in concrete if subbing out to contractor or your numbers are worthless. 3) Include sufficient vacancy percentage based upon the immediate, surrounding neighborhood 1mile or less, when doing your numbers.Plus, as a mixed use, can you get financing or can a new buyer if you sell?

No two borrowers are exactly alike, you need to take steps through underwriting each one to be compliant and avoid financial losses, like fines. 

The reason I ask is people throw around these rules like they are concrete.

If a tenant is not compliant with what is in the lease you send them a notice of non-compliance. we also have a clause that states they cannot run a business from the home I would say this is one of the more important  restrictions when it does come up.

However, I never rent to family or close friends - - imo, make that a concrete policy.