@Jared LeggettFrom my experience, house hacking in NYC is doable, but it often means looking into more affordable neighborhoods or smaller properties.

As often happens with a HELOC vs a traditional mortgage.For example, if you mortgage rate is 5%, most instances your HELOC (assuming you are using it to replace your mortgage in 1st position) rate will be in the neighborhood of 3%.Continuing to make your mortgage payment (based off 5% interest) towards the HELOC would allow you to pay it off dramatically faster - relative to a 30yr note (the impact is greatly decreased on shorter notes). 

declining neighborhood? 

That means there’s always a demand for rentals, especially in the right neighborhoods.

That will meet the 1% rule, but is it realistic in that neighborhood?

Highlight nearby conveniences and any neighborhood growth to attract interest.Focus on framing the size as a bonus that buyers get more space and value for their money compared to smaller homes.

He ended up finding an eight-plex in a growing neighborhood that’s now practically printing rent checks for him.

My strategy in Arizona has been adding bedrooms and renting by the room - currently getting 850-950/room in nice neighborhoods.

I recently moved to Jersey City and I'm interested in buying a multi-family property in the area (specifically 07302/Hoboken and surrounding neighborhoods).

That is difficult to answer because even within neighborhoods, there are B,C, and D pockets.