This area won't be unlike Channelview, Deer Park or Baytown or Pasadena.Not all that fluent in the whole B/C/D class discussion, so I cannot really offer anything intelligent for you there. 

One advantage that a C/D class property landlord would have is that they would not get a call.

I’m hanging out in the C, D and F+ area until my passive income surpasses my active before potentially buying B and A properties (I may never buy B and A, at least not as a rental)

If you were a baseball player, you start in the minors, then go the the big leagues. 

Most of these properties are considered C-D class properties for either being vacant or needing a lot of work.

Appearance is secondary, if the homes in the area have metal bars you should also have metal bars.In C/D class properties think cheep and easy.  

Side-skirting booking engines from the big players like Travelclick and Synxis would be a huge money saver.  

Stay away from Hammond, Whiting, Merrillville or Gary - unless you want to be in a B- or C/D-class property.If you ever have questions about the area or need some boots on the ground in NWI, I'm happy to help or connect you with some great people who can!

You might as well buy a CD, at least that is safer. 

That way you learn some of the players and systems.