If you're going to flip houses, you're gambling and you're playing with high stakes.

Guess if you have nothing to lose, there ain't no sense not to take a gamble.

The only way to get really accurate numbers though is to get quotes from at least three painters.  

How accurate are they? 

It's good size - 1.67 acres, I'm 99% sure there were no encroachments.The B-II Requirements includes a clause:  "Any encroachment, encumbrance, violation or adverse circumstance affecting the Title including discrepancies, conflicts in boundary lines, shortage in area, or any other facts that would be disclosed by an accurate and complete land survey of the land, and are not shown in the Public Records."

Zillow estimate value $64,500 (not sure how accurate this is?).

Actually the Starting Point, which is a MLS Realtor tool that comes up with a statistical analysis (not to be confused with appraisal, but it gives a ball park figure far more accurate then Zillow) is $162,000.  

hopefully you can find a contractor with experience who can give you an accurate quote of assessing water damage and what will need to be repaired.cost for termites may be another concern depending on how old the house is, how badly the roof is damaged - termites see open spaces for their meal to get started for their homes and food could spell trouble.

Is that 40k number accurate?

Zillow, trulia and those other sites are ok, but not accurate and I wouldn't (and don't) rely on them 100%.