Isn't it a no brainer to build equity and pay less for housing, given that I'm significantly reducing purchase costs?
To answer your question, yes! It's a no brainer that 2-4 unit properties where you live in one unit are a wonderful way to bring one of your big three expenses (housing, transportation, grocery) to zero. So the question is whether this could be the right property. My gut reaction is no- C neighborhoods have more hassle, higher vacancy and more repairs than their B counterparts. But maybe my gut is wrong so running the numbers is worth it.
Questions that come to my mind-
What would the rent be for the other side of the duplex? And what would PITI be? Does your $300/mo carrying cost include expenses (common area utilities/water/etc), vacancy, maintenance, capex and management in addition to PITI?
You mentioned that the neighborhood isn't great. Does that mean C+, C, C-, D? What kind of tenant would the other side of the duplex attract? What's the vacancy rate for 2-4 unit properties in that neighborhood? If you decide to move in 3-4 years, what are your management options? Do the good management companies work in that neighborhood? (You should be able to get answers to all the questions in this paragraph by talking with property managers.)