So don't buy rental but keep buying primary locally... you can even double your networth very quickly buy buying broken-home and flip it around. 

Passive Investment - Buying and holding performing notes for interest income and or investing in debt fund/partials ownership Active Investment - Buying non performing notes to either modify to reperformimg or foreclose for real estate ownership; “working” the notes in your portfolio; or “creating” high yielding investments through various meansNote BUSINESS - Running a note fund; syndicating notes, buying and selling notes, creating partials, brokering notes, etc. 

what’s the best way to use OPM to buy my first house to rent out?

I am retired and working on career #2 and 2 of 3 of our kids have left for college - our oldest is headed to UConn for her PhD (6 years) and instead of paying to rent, our thoughts are to do a version of a house hack with buying a house/condo and renting out one to two rooms to offset the costs of her rent.

What are some companies that buy these loans?

My brother and I have sent out direct mailers, very generic we buys houses cash with a phone number and a we buy house sign for the picture.

What are the disadvantages of buying a 2-story duplex? 

(In other words, if it's too high, then I can cancel the buy and not have to lose any money)2.

Investment Info:Single-family residence buy & hold investment.

You can't just buy a condo in any neighborhood and start renting it out weekly.