Because interest rates are higher than before you're expectations on the strategy might have to get adjusted and be more creative in the acquisition. 

You could pull out $150,000 via a HELOC at 8% interest (about market rate right now) and the monthly interest only payment would be $1,000.

I was only doing handwritten since I have the free time and I constantly hear that handwritten has a higher reply rate, but I'll definitely do more research into professional letters for my next round.

I originally bought this 40 unit apartment complex in 2021 in Nw huntsville, Alabama and since then we've maintained a sub 10% vacancy rate year over year.

They're experienced personal finance people and they have it all on 0% interest balance-transfer cards.

Rates are a challenge, sure, but so many GPs also bake in easy operating environment and assume no cap rate expansion.

If your rate was locked, then yes.If your rate was not locked, then it depends.

The big question I have is, will I be able to transfer this into my LLC which then can be used as an investment to avoid/defer tax? 

What is the interest rate on the note (s). 

You also need to make sure you get the tenant's deposit (in full) transferred to you at closing along with prorated rent.