Advice on asking for Seller Finance

[T.J. Isaacs]

MIL's neighbor called and said they are going to sell their house. Renter is moving out end of September. MIL said before she goes to market she knows someone that could be possibly interested in the property. An assumption at this point, but the house should be paid off. They were getting $950/mo and just raised to $1100/mo. House will need a little work, but should value around $175-$180k with updates. I am not afraid to ask about them doing seller financing, just need assistance on how that looks. 

For example purposes:

Offer $150,000, how much would you offer as a down payment? 

How long would you ask for seller financing? If I could fix and BRRRR, would be ideal.

What to offer in a finance rate? 

What else am I missing?