Confirm that we can use the usual offer-to-purchase contract, but with “subject to" existing financing specifiedCan we use the attorney / escrow as an intermediary for the payments, to protect the seller?

The best thing you can do is make sure you have a team of superstars - an awesome agent who understands what you are trying to do and a qualified intermediary that has an incredible track record - I know several if you need a reference. 

This is where a CPA and your Qualified Intermediary comes in.

I sold a single family home in June, transferred all gains into a 1031 intermediary, and closed on the first duplex without issue (I used half the gains from the sale as a down payment).The second duplex was never formally under contract as the seller agreed to make some costly repairs so that purchase was delayed.

Perhaps I'm not asking it right because I'm getting looping answers between my lawyer/CPA/intermediary.  

This, combined with relative opacity -- the loans are negotiated in private or purchased through intermediary platforms -- mean there is more room for abuse of fiduciary duties to investors, market analysts said.

Your intermediary should be exploring this with you or have already talked to you about it. 

its very hard to deal with a bank when your current.I did see this a ton in the desert though and I am sure it happened in FLA.folks through an intermediary buying their own home back at foreclosure sale.you risk being out bid but no one can usually out bid an owner occ.

You wil have to use the services of a 3rd party called the qualified intermediary to handle the 1031. 

They are an intermediary holding the money.