I don't own Section 8 but I would recommend you join a local real estate investing club. Here you could network with investors that do invest in Philly Section 8. I am a member and highly recommend DIG. http://digonline.org/
I have learned so much and even found a business partner.
If you plan on managing yourself, you have to take classes over at the Philadelphia Housing Authority located on Broad St. The house and / or units have to inspected by the PHA inspectors, and if there are any deficiencies, they have to be corrected, and then reinspected. PHA also allows landlords to promote their rentals on certain Saturdays at PHA. This will also allow you an opportunity to speak with Housing Voucher, not called Section 8 anymore, recipients.
As for eligible voucher holders, there are approximately 18,000 and housing is needed.
It can seem a little confusing, however, do feel free to give me a call (215) 906-6702, and I can help walk you through this.