I strongly suspect that in many scenarios, you will end up out of pocket MORE than $300 a month once you add in taxes, insurance, maintenance, and utilities. 

Can I use the proceeds of a cash out refinance as the down payment for a new purchase loan?

Also my insurance agent says it's harder for him to get insurance from good companies on old older homes, unless the electrical, roof, and plumbing and have been updated. 

I also have sewer & water line insurance provided by DEP via American Water Resources (AWR) but every time I call them, they say there has to be a clog and all they will take care of will be fixing the clog.

I could see lots of folks with limited equity and no flood insurance on their house walking away from the mortgage before spending the tens of thousands of dollars to fix flood damage.

I enforce my tenants purchase renter insurance.

We are both physical therapists and we do not find it wise to have 100% of our income be reliant on being physically able to work (disability insurance can only provide so much comfort).

Investopedia is on the right track saying that the rule is supposed to ensure it covers your mortgage, but it's much more than just the mortgage, it's the insurance, taxes, maintenance, etc costs that are in addition to your mortgage.

Then it seems it would be worth it, with the added property tax and Insurance cost ( possibly $175 / month) for a total of $652 cost.

Looking for any advice on how to proceed.