And you'll need the QI to be in place prior to close because there are specific documents and addendums needed to the closing statement to reflect the 1031.Regarding the gain/depreciation calcs those will be easily summarized by your accountant on the form 8824 that they'll attach to your 2019 tax return. 

One of the main questions I have is, if there are a few additional liens attached to the property, how are they dealt with?

Metal attached to battens over osb roof.

You can also alter or add anything you agree upon in an addendum you can attach to the contract as part of the agreement.

I found a house with an odd layout - it's a 5/3, but one bed/bath can only be accessed through another bedroom, or from outside through separate entrance.I'm looking at separating the house to create a 4/2 traditional rental and an attached 1/1 Airbnb.

See attached graphic for a sample.

You can buy a second house same day, but now technically its an investment property and you need around 20% down, but talk to your lender, see what options you have. 203k programs have a lot of strings attached ... 

He's a flipper, so I'm less inclined to think that he'll be overly attached to the property, but I see the wisdom in the advice given here.

It's attached to this love for "BRRR" deals.

Some of the attached buildings have been flipped, however, many more need to be renovated.