Owner finance deal structuring 50% equity

[Joseph Leiva]

Hello BiggerPockets community, My name is Joseph, i'm a newbie investor from Miami, FL. I'm working on my first owner finance deal and am hoping the community can give me feedback on some numbers before I approach my seller with terms.

My seller rejected a cash offer but is open to owner financing. It's a rental property on a lake, in Coral Springs, FL, and comps 300-320k. He's asking 300k, owes $150k on his mortgage, and is open to financing with a 5 year balloon payment and 75k down. He's had the same renter for 5 years and hasn't raised their rent in 5 years. He collects $1,825/mo, pays $1,655/mo (PITI) to mortgage and has $400 quarterly HOA fee.

My first question is regarding the mortgage. My title company advised against a second mortgage because end buyer wont protected if something happens to seller. My seller is elderly and lives out out of state so this may very well be an issue down the road.

If this is a problem, I would need to come in with at least $150k to cover mortgage, but seller is asking for $75k down, so I would need to negotiate with seller for smaller payment. In this scenario I'm afraid a large down payment will turn off investors. 

If that down payment is not unreasonable, I can present seller with $270k home price, $180k down- $30k to seller- amortized for 30 years with a 5 year balloon + interest

And then what interest rate would be too much? If I use interest to make up in the long run for home price reduction, I'd be offering something like 4.5 - 5 %  -- Is this too high for investors? 

If he wont come down, will I be able to market this at $300k? (I do feel I can get him at $280-$290k) If I do 2% interest on $300k, same $180k down and 5 year balloon with 2% interest, using his taxes for 2015 that were $6k and a rough number of $2,500 for insurance, PITI would be about $1,150 (I'm using a calc, please correct me if i'm messing this up) $1,825 minus $1,150 leaves $675 for cashflow. Then there's still $400 quarterly fee to consider.

Input from the community is GREATLY appreciated, and if you made it this far down the post, thank you for your time.