And then comes a point when you decide whether you want to scale up or you're comfortable with your achieved state.

@Matthew TeuschelThe "risk" with Subject To is that the owner continues to make payments.You're buying Subject To the existing mortgage staying in place.

If you're operating a short term rental that focuses on <30 day stays, you should consider a Schedule C business.The 2018 Schedule E tax forms has a box for Short Term Rentals but I'm not clear what they have in mind.

Zillow says $125 rent increase equals a move and $50 increase is a common increase for tenants who stay.

you should get your financing locked down first. you may find it next to impossible to find financing for a foreigner with those kind of down payments. and for sure heed @Ned Carey advice top of the market not the bottom look for a solid 5 to 8% return instead of 10 to 15  those are for those that live there and can stay right on top of them. 

If giving a 24 hour notice Keeps your tenants comfortable, it seems like a simple solution for healthy future relationships.

It sounds like he got burned on his first SFH and that made him stay away from them.My real estate agent suggested a refinance as well, which sounds like an ideal option. 

I'm worried about  if I should purchase  outside of my comfort zone.

The question becomes how comfortable are you with debt?

I know you have to live in each for at least a year but I should have enough saved to where I can shortly make a down payment on another property regardless of needing to stay in the first home.