Make sure you don't fall down the hole of trying to learn everything there is to know about notes indefinitely.

I seriously went down this rabbit hole for about a year before I finally figured out the real reason why some properties downtown still haven't been renovated.

If they leave windows open or back entrances unlocked, thermostats turned way up when testing the heat, Fridges/freezers not closed all the way, Bring in 4 kids who are running around and knocking holes in walls and tripping down steps (that they later blame on a piece of pulled up carpet) it all falls on your dime. 

The road is maybe one and a half car lengths wide and is kind of the gully between a couple hills with no drainage and water run off next to or down the road.  

Most REO sellers will not turn on or allow water to be turned on, or allow repairs for appraisals or before closing, most secondary market loans require all utilities to be on at time of appraisal, minimum 5 years or more roof life left, no holes in walls or flooring larger than a quarter,  or significantly soiled flooring, walls, ect. 

(nothing on paper yet)or do I eat my mistake (property will still make money) but I am now in the hole an additional 20k to start?

Going up through walls is easy, often just 2 small holes in the wall, one to drill the plate and and one for the cat, the cross piece between studs usually halfway up a wall. fishing in the direction of the joists is easy, going across them can be done with small holes spanning the joist, notching it for the cable, and then put a steel plate over it.Given that your problem unit is ground floor, it's likely you can fish up from the basement very easily for outlets using "old work" steel boxes, plastic boxes don't work with plaster on lath, it's too thick.

It had been fixed twice and the last time the roofer told me that a new roof was needed because the roof in that area has too many holes already.

This can have a loop hole if you talk a general contractor into letting you be the sub contractor and not taking pay ( you might have to grease the wheels for the General Contractor to let you do this).  

Cash-flow positive just means that the property isn't eating a hole in your wallet each month.