I am currently a full time Emergency Department RN after leaving the military with 15 years service. 

Cap-Ex is harder on you than the ROI because the ROI is more of a budgeted amount and Cap-Ex tend to be more of an emergency expense.

Analyze the cash flow, be generous with repair & maintenance estimates, and make sure you can weather rent fluctuations-emergencies-vacancies for both the long and short run.

I used a significant amount of my personal emergency fund for the unexpected repairs.

I don't know if there is a unified theory as to why Detroit ended up where it is now, but I would say it's a combination of (1) over-reliance on a single industry; (2) some epic battles between that single industry and the union; (3) emergence of the automobile industries in countries like Japan; and (4) terrible race relations.  

This creates quite the cushion for emergencies.

I then had them call 211 to have a non profit pay their back rent through emergency covid relief funds.

I like Lindahl's stuff and his book (emerging markets) but it seems that he has ramped up his personal training to a new level which made me a little iffy... a 1$ program email offer recently made me lose my interest.

I just read David Lindahl's Multifamily Millions and his Emerging Markets book too. 

If you’re dealing with emergencies or a string of maintenance issues, however, expect this number to increase significantly.