I don't know anything about the area but I can show you some of the tools I'd use to find out most of what I needed to know:https://www.crimereports.comcity-data.comusa.com/rankhttps://www.greatschools.org/Punch up all the zip codes or even addresses you are looking at in these tools and they will tell you a ton about that particular location.

Check with the HRA about their contribution limits, it's not always easy raising rents on section 8, it'll depend on the zip code.

Specifically i was interested in things such as Top Zip Codes, Rent-to-income ratio, and any other goodies. 

I'm not licensed in TN, but I guarantee you that I could open my mortgage search software, plug in a TN zip code, and find dozens and dozens of lenders doing 30yf c/o n/o/o refis right now.

Low to very-low incomes, most children in school receive free meals, high crime rate, and on top of that there are 104 registered sex offenders living in that zip code.

and what are the best zip codes to invest?

I am looking to invest in Philly, certain zip codes are hot right now and prices have been rising.

I went on city-data.com, but it only goes down to the zip code level for crime rates.

What zip codes are you considering?

What zip codes?