But I will say that 1031 will not apply, that needs to be a longer-term hold/investment. 1031 applies to rentals, STRs, MTRs that are held for much longer. 

No, banks do not allow a seller held second now a days due to risk and new guide line changes. 

I'm not into Sub2.In MN when using the SOS "fast-file" online system to form a LLC it states, CLEARLY but often missed by people, Single member LLC's are a disregarded entity and legally held as sole proprietor for all legal purposes.

We held the property for about two months, and found a seller. 

The other thing I have done in the past is held this money in my cash position within my brokerage account with it not invested. 

The loans were varied and some were able to close sooner than others and they wanted to close before the others but we held out because we needed to close all of them at the same time to avoid any last minute standoffs or complications.

Save for some unusual complications, you seemingly met all the conditions for your tax benefits.Now, to traps and gotchas.Trap 1.

I have a clause in the lease that says the security deposit will be held in so and so bank with so and so address and interest rate will be xyz.

I would put pressure on the GF to try and help get him out because they will both be held accountable for the unit.

Either1) your startup takes off and you can distribute profit fast enough to pay off your debts, or2) you find another source of $100,000 a year (which barely even starts to pay down the $300k, but might provide a better chance for a better loan), or3) you BK and possibly lose the rental houses to creditors (hopefully not, but we don’t know how they are held), or 4) you sell the houses, take the tax hit, work with the IRS on a payment plan whose interest will be much lower than your CCs, and focus on the startup.