I've used Gary Martin for several years for myself & as an agent. 

Here is what I have for the LOI so far:RE: Non-Binding Letter of Intent to Purchase 3 units at...Upon agreement by both parties, a Purchase Contract will be prepared by the Purchaser and can be negotiated and signed by the parties.Purchaser: Nia **** and Alex ****Seller: Gary *****Purchase Price and Owner Financing Options: Option 1Purchase Price-475,000 Financing Terms- $1,500 per month for five (5) years, with balloon payments years one (1) thru five (5) of $20,000, $30,000, $50,000, $60,000, $225,000; respectively.

I agree with Gary that this is likely 15-20 years.