A fully paid off property which now should be worth at least $300K with appreciation, I can access 75% of that with a cash out refi so roughly $225K - refi costs.To me, its a no brainer to do bi-weekly IF you plan to keep the house for that long AND you do not plan to refinance (rate or cash out).

HELOC until the rates turn around in a year or two.

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. 

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.

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.

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.

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

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

Currently you can find 1000sqft apartments in decent neighborhoods starting at $45k and homes starting at $60k , this is info i found online Bolivia is one of those places where people are still old school and you find the best deals by word of mouth.

I’m asking for opinions in this area since the crime rate is High and vacancy rate is high as well.