He ran up an electric bill that we kindly asked him to pay. 

if you are a beginning rehabber, this is a deal i would avoid, (unless you have experiences in other related areas or have researched this extensively or have asked experts i.e. structural engineers for their input), as 1) you don't know the prices your contractors would charge2) the estimated rehab costs are lumped under general categories (i.e. concrete, plumbing, electrical), but do you know which specifically/exactly you need to fix?

He just says he can hit those numbers if water/sewer and electric is on site.

Could someone provide examples of what mild vs extreme due diligence would look like with a 4 unit house that requires a moderate amount of TLC from the landscaping to the plumbing and electrical?

Why is it an electrical system in Jersey City?

If the electrical panel is substandard (dangerous) and they are the one who hard wired an extension cord in the attic while cutting through a major purlin holding up the roof, and the garage door doesn't open due to damage (when they hit it with the car?)

Needs to hook up electricals, order in appliances, build out closets, finish building  a shower. 

But after all, he made a great decision and it was amazingly profitable.Numbers:80k Purchase – cash 35k – Reno Roof, siding, paint inside and outKitchen cabinets and countertop resurfacedPlank floor New tile in bathroomRepair electric and plumbingHome staging 1% of sale price6 month project 165k sale price less 6k closing costs44k Profit Regrettably, this will probably be the most profitable flip I am involved with for the foreseeable future.

Holding costs can be a mortgage payment, insurance, taxes, electricity, water, garbage. 5.

During this they spent several nights at her mom's, at out a lot, and now have a high electricity bill.