You have to know your local market and your state regulations (if any exist on rent changes). 

If there is a mortgage you can still buy Subject to the existing mortgage.The owner leaves his mortgage in place until you can refinance and pay off his mortgage. 

When I dealt with RF buyer's agents as a listing broker, I found them to be low energy and not especially committed to getting showings set and followed through. 

I plan to tear down the existing structure and build a duplex.

The agent orders a title commitment from the underwriter and prepares the closing docs and emails them to the various parties, i.e. closing statements, deed to be signed, affidavits, wiring instructions. 

Also, the existing leases would have to be re-signed with the Mgt LLC. 

You can house hack your existing primary residence with airbnb or rent a room to someone..and then use that money to make additional payment to principal on your existing mortgage. 

Sellers can require no inspection periods right now as inventory is non existent and there’s buyers everywhere, especially on investment properties.

It will cost you far more in time to do these yourself. and why risk committing malpractice when for relatively small fee you can get a comprehensive database search. seems pennywise and poundfoolish to me- IMHO

The 1% rule is almost non-existent in this market.