Dont know how that is sustainable in this industry.

I back it up by actually fixing things in a  timely manner, listening to their concerns, and forgiving one late fee a year. 

I already own two homes that are my personal residences, and my DTI most likely wouldn't sustain another house WITHOUT the lender offsetting the debt with the rents to some degree - is there any other method of providing lenders with rent history that you have used?

You are correct though in your understanding that you have to go about it in a careful and intelligent manner.

The jump from 20 to 100 can happen fast if you can show investors you can handle their property in a professional manner. 

He speaks to tenants in a cordial manner, and listens to their concerns.

I, also, suggest to make sure the property will cash flow enough so you are able to refinance and place a tenant should the property not sell in a timely manner.

- Any obvious risks to investing in the area (such as non-sustainable economic growth)?

etc.I think that in this manner, you will stand out from the many other lookers and gawkers who are just testing the waters.  

Look to take the slow and steady path towards creating a profitable and more importantly - a sustainable business.Best of luck moving forward.