As you've mentioned in previous posts, commercial is a whole other animal without those restrictions. 

If you are planning to do development yourself , you need to know that condo conversions are most advanced project construction wise, as you a have to do full gut work with underpinning, building addition in the back and adding new uppper floor to maximize sqf. so if you are not into contruction world , your need to plan that your construction cost per sqf will be on the higher side.Regarding waiting for 2 years or more , Zonning in DC is constantly changing, and it is constantly changing towards restricting development.Before you could do a 3 condo conversion in most of neighborhoods  and have high ceiling condo and roof access for roof deck as height limit was 40 feet for building. 

Does anyone have any idea on how they’re getting around debt to income ratios restrictions when they’re ready to acquire their 7th or 8 th property?

As a landlord you may set a reasonable restriction on number of people.

Both....however in commercial, it is restricted to residential type properties, ie apartment buildings.

If the physical therapist “use language” violates the chiropractors “restriction language” then the liability would be on you the Landlord.

I heard from a Representative this morning indicating that a less restrictive version may be considered soon.

This is a subject that very few landlords actually understand.As a landlord you may ask anything you wish, there are absolutely no restrictions.

I'm not aware of any restriction in New York.

There are also rental restrictions with HOAs.