I know the question is mainly focused on what sorts of special protections you will need as a landlord with a lease as opposed to a longer-term AirBnB booking, so let me answer that first. 

Typical problem properties that are difficult to sort but once it is sorted usually with good upside potential.

From what I gathered, most folks getting to a million that are younger are in a random business of some sort, then placing money in RE assets.

I speak to the estate planning attorney on Wed (I have another property in Philadelphia in my name that needs to be sorted as I'm currently exposed liability wise and another internationally also in my name that I am about to start STR) so I want to read up before that meeting.Thanks!

Then there are calls about all sorts of minor stuff - and just odd behavior, like calling the gas company at midnight because they thought they smelled rotten eggs….. getting our gas shut off for a day, bringing over questionable house guests, bringing over a small dog and housing it without asking, and just overall kind of being a mess.

Borrowing with no income is ripe for that sort of result. 

They still like to see some sort of "grouping," whether it is in home style, neighborhood, SFD only, etc. 

Moreover, having a mentor or some sort of coach is an absolute must-have, in my opinion, if you're just starting out. 

@William Johnny if you only have $250-$500/month you probably don’t have enough to invest now as you would likely need some sort of a down payment and reserves.

I dont do MLS listings so it helps me sort out the best qualified leads to send letters to.