How do you structure seller financing?

How do you structure a seller second as far as term, amortization period and interest rate? I have found a bank that will alllow a seller second on a 5+ unit building. They said that of course it has to be subordinated to their loan and that it has to be stipulated that the second has to “standstill” if there is a problem with the first loan. Has anyone heard of this?

Thanks so much,