Hey Charles,
Section 8 housing can be very successful strategy. I personally have not done it but have a former colleague of mine who did this exclusively in Brooklyn, NY. There were few keypoints that he shared at the time:
1. Property condition: HUD has rather strict safety conditions that needs to be met and you have to balance requirements with practicality and cost. There are youtube videos describing how people solve this in the most cost effective manner.
2. Tenant selection: Rather tricky here because while the majority of the rental payments are guaranteed by HUD, you must collect the remaining from the tenant. (I understand that you can't forgo that payment or will be disqualified). He has a rather interesting angle due to fact that Brooklyn, NY has very limited availability for Section 8 vouchers and made it work.
3. I've looked in Philly about 15 years ago and decided against it as you need to do rather deep research where to invest. Goes block by block.