Bought one on a napkin, did a lease option and closed it the next morning.

Milwaukee is FULL of rentals that look like solid deals on the back of napkins.

The paperwork, lol, that's a functionary item and so not worth of needing some "guru", it's paperwork, I have done deals on a napkin before, literally, not ideal but hey it got the job done.

The carpet hasn’t been vacuumed in years I’m assuming, she didn’t let anyone in her apartment for 25 years and now that there’s a new owner (me) she is having a hard time accepting that I am now the landlord and I want things clean and sanitary!

An enforceable real estate contract in Texas can literally be written on a napkin as long as offer, acceptance and delivery are met

Don't put too much stock into the 1% rule, it is only a quick back of the napkin analysis of a property.

Is there a back-of-the-napkin calculation for insurance quotes for small singlefamily properties?

The basic "back of the napkin" evaluation that will usually tell you where pricing involves the NOI and a market cap rate.

I crunched the numbers on a napkin real quick and saw how I could pay off my home over a longer period of time, but reinvest the money from a cash out refi into other cash flowing appreciating RE.

You can certainly use a general expense ratio for quick "back of the napkin" underwriting, but you would want to use a number in the 40-45% range for that, just to be conservative.