We generally see a downpayment of at least 20%. Monthly payments are figured on a 30 year amortization at a few percentage points above the interest rate being given by banks. Usually there is a balloon at 3-5 years, at which time the buyer pays off the loan or gets it refinanced.
In an attempt to avoid any potentially expensive foreclosure procedures, should they become necessary, many contracts call for a deed and a reverse deed. Both would be held by the escrow company to be recorded at the conclusion of the contract. The first deed is the deed by the owner to the buyer, upon final payment. The reverse deed is a deed from the buyer to the seller. In the event of a default by the buyer and termination of the contract, the reverse deed is recorded thereby avoiding expensive foreclosure proceedings.
AS WITH ANY CONTRACT, ALWAYS SEEK LEGAL COUNSEL PRIOR TO EXECUTION OF A CONTRACT.