The third floor apartment was occupied by a hoarder and had some issues.

Or what seems crazy to me.Is it legal to create a 501c3 organization to buy investment properties and rent them out at fair market value?

I've never had a real issue, and I plan to keep it that way by doing the same consistent things as other have mentioned. 

I have not had any more issues with turnover on one type than the other.

I personally created a legally created ADU or mother in law unit. 

Most are fine with that, but a few will have problems with it and claim there are legal issues, etc..

I know there’s a guy named John Fedro who had (has-don’t know) a course for how to provide owner financing and I believe had a way to do it legally.

REALTORS® shall recommend that sellers/landlords obtain the advice of legal counsel prior to acceptance of a subsequent offer except where the acceptance is contingent on the termination of the pre-existing purchase contract or lease.

I'm sure several here has or will have the same issue in areas like mine, there are many multiunits out there. 

The challenge with the students is there will be constant issues that you have to deal with.