Since this is our first project like this, I'd love opinions from those with more experience...do you see fatal flaws with the strategy, are we missing the boat on anything huge, etc. 

I'm just feeling a little anxious about missing the opportunity to sell it and make a large profit.

I want to bring a partner in to mitigate risk and also cut down on the amount of capital needed to fund the deal, since most of these homes are in the 650-750 range.Is the logic sound here or am I missing something on how this loan could work?

That said, you do miss out on some of the benefits of a brick and mortar brokerage you might find, in my opinion.

With rentprep it looks more like a credit report where it shows each account and their on time or missed payments.  

Probably won't be cheap, but almost certainly cheaper than a surprise tax bill or missing a gap in your liability coverage.

Another week went by without a reply, so I had my agent notify the seller's agent that the tenants were non-responsive and needed to be out before we closed.A week passes, I got the clear to close, and then I received a slew of text messages and missed calls from the tenants.

I missed the duplex part.

I"m not in a place where not buying something for the next year is going to put me behind in life, but with interest rates low, inflation coming, and the shortage of houses for the near future, I feel like I'm going to miss out on stuff. 

I could tell they wanted to lip stick rehab the property and list it.That's two deals in two weeks missed out on because of price.