Might try to get a working young adult or a grad student for the house manager. 

Financial Knowledge and Decision-Making.While many American adults believed they were adept at dealing with day-to-day financial matters, they nevertheless engaged in financial behaviors that generated expenses and fees and exhibited a marked inability to do basic interest calculations and other math-oriented tasks.

Now I'm destined to invest in real estate to provide housing for intellectually disabled adults.  

I would describe this property as urban camping or a youth hostel for adults.  

It's harmful to adults too, not just kids.

I've read that the 2+1 rule is unwritten law, but it seems like that's not a hard law anywhere.I have a 3 bedroom 1 bathroom property and had an applicant that wants to move in with 6 adults total and two children.

You know absolutely nothing about the unauthorized adult. 

The more of your offers can be in cash can put you on the best side of most owners.I have been into construction most of my adult life.  

There could be added risks with renting to young adults in college, but those risks extend to any potential tenants.

I have spent my entire adult life in the construction business.