@Tyler Brown, you will be hard pressed to find a duplex in Philadelphia at your price point of 40k-55k that only needs cosmetic repairs and will rent for $500-$700k per unit.While you may find a number of duplexes online at your price point they are neighborhoods well outside of the Center City District. 

Talk to the software engineer who earns 200K+ per year and cannot afford a SFH in good school district :-)

We knew a house we would rent that’s big enough for our family in the right school district and all that stuff would eb about $4500/month + utilities, etc.

In Arkansas, they asses home values yearly for special district taxes like medical, schools and any special tax districts.  

But my main point for talking about this is I could do what John did and I could do it from Portland.. since these were A class rentals brand new in neighborhoods of 90% owner occ and the very best school districts in Mississippi ( which is a huge deal) I got top flight tenants with 700 plus ficos NO section 8  ..

I am not involved in this particular market but I have a good friend who owns her personal home near the heart of the movie making district in Atlanta and she says there is huge demand!

One other suggestion is to always look up your contractors license on the state licensing website and look in the General District Court and Circuit Court websites.  

I also spent cumulatively 4 or 5 years living in boarding houses, mostly in U district during college,  and some ran batter than others.1)  I would not try to go past 8 residents.   

Its important to be mindful of the average cap rates within each sector and on an apples to apples comparison, meaning you can't compare office space in the financial district with retail in Long Island. 

Some of the areas I'm considering in Houston is Midtown, Museum District & Montrose.