May plan is to pay cash and wait until interest rate improves, then refinance and pull out $150k for a down payment on a second property. 

See Nobel prize winner and associate  quote....Gunner Myrdal, an architect of Sweden’s welfare state who was given the Nobel Prize in economics as the left-wing balance to his co-winner FA Hayek:  Myrdal stated, “Rent control has in certain Western countries constituted, maybe, the worst example of poor planning by governments lacking courage and vision.”3 His fellow Swedish economist (and socialist) Assar Lindbeck asserted, “In many cases rent control appears to be the most efficient technique presently known to destroy a city—except for bombing.”Seattle is a prime example.

Is that still a plan?

For each of the personas (enclosed), we have a different action plan. 

Plan is to purchase assets in the Louisville area to start but open to funding deals in other markets.

And the second duplex hasn't appreciated sufficiently to take advantage of the capital gains exemption yet, so planning to hold for the next few years.For this third duplex, however, I would like guidance on how to title it:1) Given that I am paying cash, and I am not totally sure I will sell this within the "2 years in the last 5 years" rule, should I just put it in a LLC rather than my personal name (thereby missing out on the gains exemption)? 

We plan to use short term rentals to cover the mortgage/monthly payments but with the skyrocketing property taxes in that area, I'm concerned we may not be able to net enough. 

You will almost always pay more than you initially planned.

I plan to do cost seg study and get bonus depreciation (and will actively participate as per IRS rules) but need to confirm if this would still work if buy STR under LLC and I can still be eligible for that STR loophole?

Plan to sell all POHs, seller financing, or cash sales.