So I am looking at this as a way to decrease my federal income tax if I lose FEIE.

(assuming the cash flow is higher than PITI).My second question is if I acquired a duplex via seller financing, would that also decrease my DTI?

And lastly, I search FunishedFinder listings nearby, find comparable properties, and track the listed rent for a few months (does it increase, decrease?).

As supply increases, demand decreases, which can eventually lead to lower prices if done on a large enough scale.Unfortunately, many people outside our industry don’t fully understand this.

Let me explain that better, imagine your rehab is $100k, you would need to do part of the rehab, maybe $10k, and then you can get the funds for those first $10k reimbursed so you can keep progressing with the rehab.Given your experience, I would recommend you start with a moderate or light rehab, mostly cosmetic work so that you can do it yourself and won't get your profit decreased by hiring third parties.

As a result, my profit decreased as buyers began negotiating for lower assignment fees, using the leverage they had developed.

If you are changing careers and your income will go down significantly (you said change, I implied decreasing), why not keep the money as a back up/emergency fund in case you need it?

I am not on the forums enough to notice but as rates decrease, loan transaction volume will increase. 

So, I believe some of the fundamentals of larger multifamily (increasing NOI via increasing revenues or decreasing expenses) are beneficial to smaller multifamily although the ultimate value is not determine by NOI, but by comps. 

I increase their ROI in the process and decrease risk/headaches.