This is from the BP rental calculator and is exactly what I'm wanting to see, just with extra payments each month. 

That's tax-free money, but your rents need to be able to support the new mortgage payment.

Utter blasphemy, only "unsophisticated" investors buy in cash.An experienced investor once told me "why use my cash, when I could just default on OPM" I know its not popular thought on BP.. and of course ramp up requires it unless you inherit a ton of dough but as we age out I sure like free and clear and no debt.. just the hassle factor of having to make payments :)

There was also a loan grant available from the state of NH for first time home buyers for 3% down payment assistance.

Your payment requirement would rule you out for us. 

Monthly payments are fixed.  

We refinanced and cashed out all our renovation budget plus $5,000 and actually kept monthly payment the same as rates had dropped.

That's $1680 per year for QBO, plus my Bookeeper at another $500 a month to log monthly statements, break down loan payments, and reconcile.

To me, having one mortgage payment for 2 - 4 houses (basically) always seemed interesting and like something that would give me more bang for my buck. 

There will be late payments and defaults etc.