owner financing on a duplex

[Zac Boelkow]

So I have an offer in on a duplex. Owner is asking 175k I offered 150K. I require financing, which I am already pre-approved. Bank financing is 30% down and roughly around 4.5-5% on a 30 yr note. The duplex is rented, under market value at $650/month. I would raise rents $100 ea side in hopes that I would not lose the tenants as they are long term tenants. If I would lose the tenants then rents are more likely to be 850-900/month.

The sellers agent said the owner would take my 150k offer if he finances the property. I asked what his terms would be and it does not sound as if the sellers realtor or the owner have ever done an owner financing sale as of yet. My realtor told me to just come up with the terms that I liked and we'll submit the offer this way. We did already tell them that we wanted similar terms as we are getting from the bank. The only exception is we are only putting down 20% with owner financing. 

Any suggestions/tips/advice will be helpful. I have never done an owner financing before either. It doesn't seem like its too complicated. Since the seller is asking me for the terms I feel like that puts the ball in my court. Thanks!