Motivated Seller is READY! What do I do?

[Troy Cole]

I have an owner occupant/ seller who is willing to carry a note on the property at $20,000. It's worth easily $40,000 fixed up though he pays taxes on $50,000. It needs about $5,000-$6,000 in rehab and will rent for $500/mo easily in the area. I feel like this is a good deal and probably will be my first one but I don't know about notes and how to write up the contract for those. I'm trying to get in touch with my lawyer now but it's the weekend so maybe by Monday I'll talk to him. I just want to know what would be a reasonable down payment and terms to offer him on these numbers? Somebody please help! Any and all advice is appreciated.