Here's an article with some examples: https://finance.yahoo.com/personal-finance/one-extra-mortgag...You can also search for "early mortgage payoff calculator" and enter your own numbers to see how extra payments impact your mortgage.

The cash flow to LL using PM for STR is not substantially different after including extra expenses than an LTR.  

Paying a plumber extra for an off hours call runs your bill up.

They have actually paid down extra principal every month.

So would this extra layer give me any help?

Many sellers were skeptical of FHA financing because of all the extra steps.

The reality is the opposite - if it's not in writing then the PMC doesn't have to provide the service or can charge extra for it!

And I just gained an extra 3 houses that my new tenants are paying off for me.

There are many maybe 80% of them will not share much information with investors or landlords, it’s not their job and frankly that’s just extra work for them the case workers.

I'm wondering what am I allowed to do with the 150 square feet besides ingress/egress.For example: Can I add 150 square feet to the structure, including an exterior door, and then use the extra 150 square feet for a kitchenette?