We got an interesting proposition - will this real estate deal benefit us?

My husband and I work full time and make about $26,000 year. We have a $90,000 mortgage and would like to buy a rental. We have $15,000 in savings (was an inherritance) and would like to devote it to that purpose. With those numbers, however, we can't get a second mortgage because while our credit is good and we have no outstanding debts, we have too high of a debt-to-income ratio. The man who sold us our house, has offered to sell us the neighborhing duplex with no money down. We would lease the house and it would remain in his name, and we would maintain it and collect the rent and choose the tenants.... until we could start paying the mortgage ourselves and then take over the mortgage someday. The duplex rents for $500 a side (or $1000 total), and he says we can pay him $500/mo and keep $500/mo. We would also have the advantage of choosing our neighbors and ensuring a good neighborhood, which is a BIG PLUS. Is this a good plan?