Keep in mind, I was still responsible for urgent repairs/habitability even though the tenants were there illegally. 

If they aren't paying other bills, you have no reason to believe that they will break that habit and pay you. 

I'd definitely check out High Performance Habits by Brendan B, Book on Low and No Money Down Investing by Brandon Turner, and The One Thing by Gary Keller.

Apparently, this is a habit for him!!

After the first few months of setting money aside it became a habit and it was easy to save money.

It seems to be merely 1 billion people finally having cash to catch up on consumer spending habits that we've been accustomed to for the last 50+ years in North America.

As co-habitants their rights are joint and providing a key to one is the same as providing a key to both.

A slumlord describes the landlord who doesn't maintain the property up to building code and habitability standards, and who doesn't respond to tenant requests for service and maintenance.The location of the property, amount of rent collected, value of property, or income of the tenant is NOT what defines a slumlord.

If you simply mean it is an traditional residential investment loan, no harm no foul.

It's just a little greasing of the palms and as long as there's no harm and no disturbance, everything is smooth.