I know there's some thought out there that you should cultivate direct relationships with insurance companies or construction companies, but  that's tying yourself to one industry when the platforms like Airbnb or Zillow are where a much wider pool of potential tenants are looking.Long-winded rant aside, I bet Atlanta has a great market for MTRs (and probably STRs if the laws allow them).

What will happen when the credit card companies and banks tighten their lending standards?

I asked the insurance company what happens to him if it’s unlivable and they said they will reimburse me for missed rent, but if he is displaced it’s on his renters insurance policy to pay for hotel or whatever he decides.

The principal and interest payment will remain the same, but the loan payoff date will be escalated as you make extra payments towards the principal.The details of your monthly payments should be available on your monthly mortgage statement as it lists the principal, interest, taxes/insurance escrow, and PMI paid that month.

We just purchased a Quadplex and were sent an insurance quote.

Paying zero tax is inefficient in it of itself--- unless it was for the rest of my life or something...Making use of the lower/lowest tax brackets and the standard deduction (being so massive nowadays) is a huge tax break in it of itself.As mentioned, you only drive one's taxes higher (and/or higher tax brackets) in future years, especially with using up the depreciation faster. 

Booking.com does not provide any insurance like Airbnb does. 

Their source of income is critical as they have no backstop (sick days, health insurance, etc).

@Jack WoodwardWhat are you concerned about being sued for that would not be covered by insurance?

In Fort Worth, for example, payment standards are listed here, plain and simple.