Need Help structuring a Seller Finance offer/ newbie

I currently live in a rental and I would like to ask the landlord to do a seller finance. Some facts about the property, He has had the property for 14 years, so plenty of equity. Last time I spoke with him he wanted to be sure I was staying another year when my lease renews in July and promised to only raise rent $25, which he held true to. I just received the offer of renewal. He is concerned about tenant turnover (Pain point.) He is 89 Years and I believe the home is in a trust. I would like to offer him a 5 year or 10 year seller financing option for his steady payments that he wants while giving me a property to start real estate investing. My question is how do I figure how much to offer him in payments for the time period and would I just offer the balloon at the end of the term? I am not sure if he would be willing to do this but figure it is a good opportunity for me to practice negotiating. I currently pay $1600 a month. Escrow and reserves is $440 a month, I was thinking of offering payments of $1k a month and 5% interest for the 5-10 year loan term? The reason for the lengthy time is he has given me the impression he relies on this income to sustain he and his wife. This could be a solution for both of us I feel. Thoughts?