What I don’t understand is how to navigate seemingly vast distance between concept and hiring a qualified contractor.

Although i have reasonable amount of cash to get this business off the ground, i just struggled to get the numbers to work (ie sufficient cash flow from buy and holds to support my life without a W2 job). 

Protecting their credit score is sufficient motivation for most high credit score tenants to play by your standard lease rules.Low income tenants are playing by different rules.

The vast majority of units that we bought were picked up at around 45% but they stabilized at around 25%.

I would take a look at your management agreement there may be a termination clause and possibly termination fee I would also take a look and see if there is a 30 day notice required I think probably something in writing should be sufficient but again verified by looking at your contract 

It'll vary vastly depending the tenants, how many people live in each unit, whether or not they're employed, and whether your fixtures are water efficient. 

In my experience, the vast majority of people with emotional support animals are under 30 and lower income.This is just one example of how weak our culture has become.

Seems like that would be sufficient proof. 

Based upon this I would look at an actual dollar amount, not percentage that: 1) enables you to live in a safe neighborhood and decent schools district, is modest in size and fixtures, and has payments sufficiently small that you are still able to invest at least 10-20% (or whatever your target is) of your income. 

My guess is your original contract with the seller is not sufficient.