It's kind of the same with an auto mechanic for example. 

I believe mechanically fastened? 

The downsides are high turnovers since many are based on a subscription/auto payment model.  

The actual mechanics and nuts and bolts of it are not really that hard, but the hard part is getting clients.  

I have a history in auto and homeowner insurance sales and a little in claims.

These things will make the mechanics of tracking and follow-up effortless.

Curb appeal, mechanical systems, or actual unit upgrades?...

Not liking the lower cash flow but It's a savings mechanism that to my understanding I would save on taxes along with placing money out of reach (reachable but with the way I am a lot less chances of approaching than a regular account).

With 20% down, a 15 year note would cost $10,800/year.  30 year note would cost $6840.We don't want to make the same mistakes we made when purchasing our auto business.  

(Think auto factory shuts down in a city where it is the major employer.)Is there a generalization that one factor like dropping oil prices will affect real estate in X way?