If it were me personally, I'd rather buy 4 rentals in cash, collect 6K/mo in rent...and have $50K sitting in the bank to start off....not too bad if you ask me.

Well, it could increase it because you're collecting more rent, it could decrease it because you have more expenses and/or more paper loss (i.e. depreciation), or it could all come out in a wash if your increases in rent approximately match your new deductions.Let's say for 2020 you have $100,000 in profits that would be taxed at whatever your tax rate is. 

From my understanding of contract law, his failure to enforce the late fee for so long would waive his right to collect it.

After 6 months of him being on time, I sent him a $50 gift card thanking him for helping to simplify our rent collection.

I’ve been able to run a very successful Airbnb out of this property and collect rents I could have never imagined at first.

They even pre-screened the tenant and are collecting legit rents.  

D class properties may look good on paper with numbers but actually collecting the rent becomes a lesson in frustration and wanting to quit. 

I appreciate your personal experience of never going against a borrower on a guarantee but it is inconceivable to me that a lender  would forego collecting on a deficiency when assets to satisfy a judgment are available and legal fees are not a deterrent.  

We would like to start using Cozy or Zillow Rental Manager for our rentals to collect payment and screen tenants etc.

Perhaps you can collect an additional deposit for utilities to raise your deposit monies.