I am currently renting at 40% below market rate rent and will be putting 5% down. With my low rent when I calculate the numbers for a duplex I would pay the same I pay in rent while I live there. I don't really want to tread water, or worse go backwards. (I'd still be putting aside the 15% as if it were fully rented because of Murphy's law)
I'd have to live there a year, then move (another duplex?) so I could make $400. I calculate that a quadplex would make my effective rent $350 below what I'm paying in rent today and when its fully rented it would bring in $700.

It takes longer to get the quad but it has a positive effect on my saving rate versus treading water in the duplex which requires me to move to "make" money. The money I pay in rent for the extra time is offset as soon as I am in the quadplex for 16 months. 

I also know that a duplex, while slower, is the safer, more conservative approach and on my single income.

Either way, for the second property, said another way its like small steps every 16 months or bigger steps at 32 months based on my current saving rate. I know I should be focusing on the first property but the analytic side of me wants to plan out two or three house hacks here and then move, in six years to a duplex hack in six years, in Asheville NC.