I'm looking at a roughly 2,800 sf house in the Kent, WA area, about 20 minutes from Seattle. It has a MIL apartment below that is a studio with it's own laundry, kitchen, bath and garage, separate entry, etc. The house is three stories so I would live on the top two floors.
Between what I could get for the MIL apartment and principal pay down/tax benefits, I would make $500 more per month on this house than I would buying two houses.
Still, if I buy this house I get two rentals; convert my current primary into another rental and the MIL, moving into the top floors myself. My after tax and principal pay down as well as rents from the MILA, my housing expense for that house then comes down to $400 a month without getting a direct room mate, and I'm still making money from my current house that would then become a rental.
If I bought two houses and moved into one of them, I gain two rentals, but my after tax and principal pay down payment is about $1,300 a month for the house I live in. Each rental pays about $600 a month in profit.