They do not work well for tenants as they easily block causing you many late night calls. 

That's something I really need to work on as my current guy that i have used all of my adult life is a retired guy from a big 4 who is more or less an H&R block.  

Only because Philadelphia is such a "Block by block" city that some "war zones" share the same zip code as A-B rated areas (Example: 19104 Is the Mantua section of West Philadelphia, but is also home to Drexel, and UPenn (Also known as University City)

Philadelphia can be very block by block, especially some of the neighborhoods you've mentioned. 

Financing sounds important, but I think a more important question is, what kind of tenants do you expect want to rent on the same block as a boarded up townhouse?

My main question is about the basement, about a quarter of it had concrete, but the rest was gravel.

I know they can raise and level concrete.  

In the few blocks around me, older houses are torn down, new ones build, and sold for over $1 million, now more.

The surrounding rents of at least two other duplexs within a blocks radius are renting for 1k a month on each side.

First l advertise cross streets a block away never exact address, second if someone call I will pre-screen them over the phone; does the price work for your budget, what do you do for a living, can you provide paystubs, can you pass a background check etc. then because I use lockbox most times I never give the code until first they send me a picture of their drivers license and second they are at the house with the lockbox in there hands to prevent them from even writing it down.Also they must call me back as soon as they are done looking before they leave the property for security reasons, make sure the keys are back in the box and combination is shuffled and of course to tell me what think about the place.