Install new drywall in property as and where needed, mud, tape, sand, and finish.

The basement is open with a full bath (we recently added during a sewer upgrade); the 1st level contains the kitchen, living, dining, and mud rooms; the 2nd level contains two beds and one full bath; the third level contains two full bedrooms (a large, nicely converted attic). 

Several things are red flags: the low purchase price, especially for a duplex, almost certainly means one or more of several things: it is in an undesirable neighborhood and it will be difficult to manage, they didn't do much on the rehab and it will have some very significant differed maintenance, it will be very difficult to exit without a loss because it won't appreciate. 

I do this with undesirables moving in to my units.If you can serve the notice the police will arrest him for trespassing.

Large flat walls are cheaper than small areas with lots of cuts & corners.It will take a small crew about 7-10 days to hang drywall, tape and mud, then let it dry a day or two, then sand, mud again, dry again and sand again, finish and clean up.

Include property manager (normally around 10%) if you plan on having one.I agree with the previous poster regarding the foundation...we had to have a house mud-jacked in FW.  

But when I compare this investment versus trying to house hack in an undesirable neighborhood of Brooklyn it seems like a no-brainer. 

Buy undesirable wetlands, marshes, and DEC protected lands that could be sold for pennies on the dollar.  

Pop out your last row of tile, set the edging and re-mud your tile.

Split level 1800 sf and need to refinish all the upstairs and tape / mud / finish the lower level.