Seller Financing Down Payment

[Derek Tellier]

This is hypothetical but based on an actual property I looked at but I'm just practicing analyzing deals and wondering if any this makes sense...

I have a property that's priced at $100K, needs some exterior work totaling $10k. ARV $125K.
I'm approved for 80% but don't have the other 20% available.

The seller was already offering to do owner financing if he got a  down payment, since I'm getting the 80% from a lender I'm going to assume they'd finance the other 20%. 
I assume this would be no issue with the lender, or would it since I'm not actually personally bringing anything to the table? Or as it pertains to the lender am I really just buying the house for $80K? 

Let's assume that all is a go and the buyer does the $20K at 5% with interest only payments and a balloon after 2 years. Within that 2 years I refi for $100K to pay off the buyers 20K. 

Running all the #'s during that first 2 years I cash flow $215, after the Refi I'm at $195 since I no longer have to pay the interest on the $20K but now have a 30 year loan on $100K instead of $80K. 

I'm trying to think creatively here, in this scenario I'm out just the closing and rehab costs up front. In the end I realize I don't get any equity out of it but I'm cash flowing almost $200/month. 

Does any of this sound reasonable? 
Thanks for any input