Electric is easier if walls are open so it is a cost.  

I currently work full time as an electrical apprentice but will be going for my license within a month or two.

I am a union electrical Apprentice so I plan on putting in a lot of sweat equity into the property.

Or should I be planning closer to $100K+ to cover hidden issues like roof, boilers, plumbing, or electrical?

With that method Id have to pull out all the electrical boxes to compensate for the thickness of the new drywall (probably the second cheapest). 

My biggest challenge from my previous attempts was finding reliable contractors who actually show up and finish.For those of you successfully doing volume rehabs in WNY, what is your single best piece of advice for securing a reliable general contractor or a strong network of subs (plumbing, electrical, HVAC)?

So over the last year I dealt with houses with roofs with gaping holes in them, mold damage, rain damage, broken sewage pipes, stolen water heaters, an ancient electrical panel that had caught on fire, my grandmother's metal shed being stolen by a hoarder tenant, my dad also being a hoarder, and even some fun squatters.

Quote from @Jacob Guereca: Recently, things have started to gain real traction for my General Contracting and Electrical, There’s nothing I wouldn’t sacrifice to protect this opportunity.

Any surprise “gotcha” expenses (sewer connections, environmental cleanup, electrical upgrades)?

The (notorious) electrical utility now requires me to have a special license to dig trenches for underground conduit, it includes a behavioral test....so im nice to their workers. 2 months of portals, videos & testing + $500 annual fee.Im not a fan of ban culture, someone always goes around it somehow.