Short of specific decisions or clear law, the distinctions seem extremely vague, arbitrary, and a bit scary.

Is there a distinct line on when you have to do that (relationship with investor, amount of money, size of deal,etc.)?

They stole over 2000 deposits and were so nefarious that American Greed did a segment.  

Making a different LLC for each new property further segments and limits any potential liability between them.

@John Warren yes, that's a good distinction.  

My focus when selecting properties is to buy only those that my target tenant segment is willing and able to rent.

We NEVER add to people's posts, just remove either entire posts, or segments of posts that pose a problem.

When you hear about landlords not receiving rent due to the covid eviction moratorium, this is the tenant pool segment most are referring to.Permanent - These are typically families with an income between $45,000 and $65,000/Yr.

If you go with 30% or 25% of income, then you'll be affordable to an even larger segment.

In my friend group, nearly all who rent could afford to buy.... renting simply fits their lifestyle better at this point in time....I think that's an important distinction.... it's not that millennials can't purchase a home.... it's that they choose not to.