Nothing was working from plumbing to electricity.

. #3 hydronic boiler could also do your domestic hot water.

I'd be concerned about the remaining lifespan of the property's major components (roof, foundation, HVAC, electrical, plumbing)

The plumber that fixed our plumbing disaster (around the base of a toilet) recommended I reach out to a carpenter to check for wood-rot.

Also, it's likely that the electrical and plumbing systems would have been treated with a similar level of care (i.e. it's unlikely that they'd neglect the electrical and take excellent care of the plumbing, or vice-versa). 

Within a week of him moving in, we had numerous complaints from neighbors and the HOA about loud noises like domestic abuse, etc.

Every decade has it's own points of concern including heat, electrical, plumbing, insulation and foundation.

Plumbing plumbing plumbing has been a major issue in this property, it’s one thing after another and by now I’m in it for like 3k just in plumbing related expenses and the plumbing issue is still not resolved!

Replace the plumbing, electrical, roof, and water heaters and you'll probably see the rates drop significantly. 

Another contractor upgraded our plumbing and then had an astronomical price to do the electrical upgrades that were not included in his estimate.