Estimated cost for remaining changes (all new electric, drywall, tile, fixtures, cabinets, roof, doors, windows, heat pump, some siding, and fencing.

Glad you are setting aside money, but if the HVAC is 20 years old, or the septic system has never been pumped, or the roof is 25 years old, etc; you will get hit with a cost before your build up enough set aside.How stable is the other tenant? 

What happens if the roof has to be replaced?

Like deferred maintenance, (bad roof, worn out water heater/AC Unit, warped flooring, water damage) etc, unpaid utilities,  unpaid taxes, a second loan, unpaid HOA fees, a bad pool, bad reputation, sometimes squatters, sometimes they were drug houses, and so on.

Our plan was to rent it for 3-7 years, and then sell it, before a roof, HVAC, plumbing, or even much flooring was in need of replacement. 

Now, with those out of the way, you can worry about the roof, foundation, sewer, HVAC, pool, etc, because these don't matter at all if you can't get the property sold.8.

The cost is the same for a roof on a house that rents for $800 per month is the same as on that rents for $1800. 

It is important to find something that was properly maintained, with modern plumbing, electrical and roofing. 

Lets say you needed $100k in financing at 12% + 2 points and it took you a year to rehab and refinance that is an extra $14k + closing costs.2. you mention roof is 18-20k.

People were panicking about their roofs collapsing and willing to pay almost anything to get someone up there to shovel them off.