Any success stories or, dare I say, horror stories?

Plenty of successful investors started right where you are.

.- We also negotiate a reasonable completion date, depending on the Scope Of Work (SOW). --- Who gets all the phone calls and wastes time calming a tenant down because the owner's contractor doesn't show up as scheduled after they took time off from work or a 3 day job takes 3 weeks?

If he doesn't need the cash now, you could also negotiate a split you're comfortable with to get him the return you and he feel he should have at the point you refi when the balloon payment comes due. 

Lastly, the barrier to being a successful landlord is getting slightly more difficult (still not wildly difficult) year over year due to tenant friendly legislation being passed.

How did you find this deal and how did you negotiate it?

Focus on learning how they generate leads, negotiate deals, and close transactions.

Or you could try negotiating hard with the seller—point out the comps and the condition of the property.

Awesome to see a new investor-minded person here.. do you have a favorite real estate success story already?

I would negotiate a price point that is lower - maybe the 10-12% range above "market".