How do you organize seller financing?

[Matthew Scott]

I am new to investing and after flipping a home I was able to use that money to purchase a duplex that I am adding value to and living in for free because the tenants pay my mortgage. There is a family friend who is helping his daughter sell her house in my area. He has a lot going on and I think he sees this property as a nuisance. He is also aware of what I am trying to do with real estate investing and is supportive of me. All this seems like a perfect opportunity for me to approach him with a solution that benefits both of us. 

I do not currently have the income to qualify for financing for the 300k selling price he is looking for. My hope is that I can come up with a seller's financing option. I am thinking maybe a 30 yr fixed rate with the option to pay it off after 5 years. So they would receive monthly payments from me and after 5 years I can refinance and pay them off. 

Is this a plausible idea or too far fetched? And who would I contact to help right up the paperwork to complete seller financing?  Any advice is greatly appreciated.