I'm reasonably handy, but not to the point that I would try to gut and rebuild a house at this juncture.  

The previous investors assigned gutted the property, and hasn't been back!

My experience is you can keep tweaking numbers to justify it one way or the other, but the gut feeling along with what you see in the area and how you feel about it matters a lot too.

My first instinct is to structure similar to a hard money deal, refinance and pay him back quickly.  

And if it's about the same, trust your gut instinct!

I don't work in your state but my gut tells me they are going to be really close in price to each other and all that calling might only save you a couple of Ben Franklins but lose some hair in the process.  

@Joseph Ball I love San Diego, Oklahoma City, Orlando, Jacksonville and Atlanta, mainly because Tampa seems to be cresting a retail saturation that may leave us in an overpriced market for a little while; just my gut.

My gut feeling is that the building will turn out to be encroaching on the back neighbors property.The neighbors property was built in 1956 and the current owner has owned it since 1976. 

My gut feeling is the total number of seller financed notes (1st position, over $30K loan balance) is flat year over year.

I'm a soldier in the United states army in the brink of retirement and I wish I had the guts that you are displaying to get started in this business at such a young age.