Although I’m sure the bank made it clear that rents would have to go up quite a bit in order to meet the monthly mortgage obligation.

As far as the sale of a property with a mortgage on it, that all gets sorted out at close. ie, you bring your money, the bank gets what they have coming, the realtor gets what they have coming (if there's one involved) and the seller gets the rest.

If there is any kind of damage to the house because of a natural cause if you approach the insurance company without a landlord's insurance they will outright deny your claim.If you have a mortgage the bank will insist that you have landlord insuranceTenant has renter's insurance.

What it appears matters most is who the issuing bank is. 

Credit unions or smaller regional banks might be a better fit.

Also, why pay 3 times the price of a house to the bank?

It’s a bonus if the bank offering the HELOC also handles BRRR loans — they’ll be more flexible and accommodating when it’s time to pay off the HELOC with a new loan!

It markets our properties, screens our tenants, collects our rent, deposits it into our bank accounts, has full accounting and reporting features, has a tenant facing web portal & app where tenants can log in and report maintenance issues and see their account, etc, for $2/door/month - but they have a $45 minimum monthly fee... so up until you cross 22 doors it would be $45.

See the attached maps of his/his related entity real estate investments (courtesy of The Wall Street Journal). 

Credit Union, Brokers, Banks (all have different advantage & disadvantages).