Code for your area may include plumbing, electrical, bedroom windows (proper height, width and clearance for egress), some areas require sheet rock around the heater and hot water heater. 

I anticipate future problems with the property, there’s foundational and electrical problems with it.

Other considerations things to look at include; are any utilities common (like paying for a boiler for all 4 units instead of individual furnaces), how does access/common areas work, do the tenants all have access to laundry, are there any common area utilities (light common area lights, electric or gas for laundry) that would stay in the owner name.  

Based on the costs of infrastructure, water, sewer, electric, roads etc. a investor will be deep into debt for a long time before lot rent will even come close to covering debt servicing. 

Call my buddy Gabe at City Electric. 

The house's electrical system seems to be functioning properly, but given its age, we're wondering whether it would be beneficial to replace it entirely( I.e update the whole electrical system) My question is this: Would installing a new electrical system increase the value of the house and make it more appealing to potential buyers?

It should not need much in the way of electrical, HVAC or plumbing.Can this be done for between $60-$100k?

I like to point out to my potential tenants that I added insulation or replaced a FPE electric panel to show that I don't just slap lipstick on my properties to make a quick buck....I would think the same would be true of appraisers.  

Anything built before the 70s will most likely have issues with plumbing or electrical, and roofs last about 20 years, and should be permitted most the time on county websites. 

Here are some other facets of a rehab which may be more expensive, roofing, windows, HVAC. electric service exterior and interior.