I'm not sure where you're located but chances are your state requires the new owner of the property to honor terms of the existing leases.

asking all the veteran STR owners/managers. what are the things you would consider including in new construction being built for STR?

You can run your numbers and try to find/contact the owner(s).You can work to get the property under contract without a real estate agent unless you want to exclude yourself from the headache of paperwork.

The owner is remote, and there is one main person running the business locally, so the challenge is how to replace this local person without losing existing business/clients (no, this person is not looking to stay for the long haul).You all sound like very experienced managers. 

There is also a house onsite that the current owners live in and manage the business from.

In almost any city with a large enough population owners can build a permitted ADU on any residential lot.

in NYC some owners are known to rent out their semi basement which is on a grey side. so during inspection would that cause any issue?

Are there any sites you use to find owners open to subject to?

I have helped owner occupants use down payment assistance programs to cover the 5% down payment (in MO), and then negotiated seller paying all the closing costs.

One of the biggest concerns for both the owner and the property manager like myself, is getting paid.Many guests book for much longer than 30 nights.