.), would you take the risk to buy it with under market price (knowing that the existing tenant can live there for another 20+ years?)

Most note investors originate new notes or purchase existing notes (sometimes at a discount to principal)..  

@Robert Dunbar Free options do exist!

And do you think 2,500 is sufficient for the four existing bedrooms?

DC is where the most multis exist in the metro area. $650k ypu could be in Deanwood, Anacortes, and those swaths of SE and NE DC.

There’s a lot of misinformation out there that is presented as knowledge.One can do a reverse exchange where one buys the new property first and then sells the original property after - all via a 1031 process. https://www.investopedia.com/terms/r/reverse-exchange.aspReverse exchanges do exist and they are “legal”. 

If CD's were better, how could "O" exist and pay what they do???? 

As I am doing this, can I start to ask my existing tenants to sign new leases with the LLC and make payments to the said LLC or do I need to wait till everything is done. 

The property is an existing STR and the historical P&L data is solid.

In some situations, a landowner might be able to purchase beds already with a license from a an existing assisted living facility.