The bank will want you to be working for a certain amount of time and that have certain credit score plus have your financial ratios match what they want. 

Don't know how many times it's been mentioned on here, but the modification of any mortgage is a new extension of credit legally.

We're wondering about various what-if's though, such as what if the people tear up the place, what if we don't want to rent to someone in particular due to references or credit or pets, etc.

My socials are terrible, so I am not the best one to take advice from on here but wanted to talk about how it has helped me.

I don't accept credit card payments for this very reason.

If your rate is low on the 5 unit, I might consider the possibility of a line of credit for my equity instead of an entire new mortgage.  

I have taken all my taxes and insurance out of escrow, and I run them through credit cards to rack up points, so I pay a lot of bills every year.3.

I called Home Depot, they told me to dispute the credit card charges so I did.  

One of the things you can start doing is reviewing your credit score and work on improving it if needed.

We bought it for $225k with a 3.125% mortgage and 1) are interested in keeping it as our first rental. 2) We are thinking about using some of the equity (maybe $50k or less as a HELOC to combine with existing cash for our next home down payment that we can convert to a HELOAN through our credit union).