On the topic of Columbus though, the city actually has a pretty diverse market when it comes to 1-4 units.

You pay for the amenities and the diversity in culture.

He is not familiar with a self-directed IRA.A self-directed IRA is still a tax sheltered retirement savings vehicle, just with the capacity to invest more diversely than just the stock market. 

My criteria for picking the state to invest in is as follows: 1) Landlord friendly state 2) Low Property taxes 3) Low median home price4) Positive population migration/growth5) Diversity of employmentSo far I'm considering states like Ohio, Indiana, Alabama, Kentucky, Missisippi, and Tennessee.Any advice or insights into any of these markets?

Much more diversity in terms of jobs by industry than any other metro area in Texas.

Reasons I like multifamily vs retailI have a more diverse customer base. 

As mentioned above, Atlanta is a large and diverse city so it depends on your goals.

I do think there are many upsides to a partnership as a team allows for diversity of skillset, funding, and responsibilities.

Job growth, population growth, diversity of industries, etc.

It does make management for us a bit more work as we have to manage both Rhino and security deposits, but we've concluded that this is the cost of doing business when we have a diverse portfolio of price points.