If the house has serious problems (foundation, mold, leaking roof, busted mechanicals, plumbing leaks, etc.) or is in the middle of nowhere or otherwise in particular location/market/situation, then you have to wonder if it will get rented.

(old widow house past away) this may be a nob and tube house in my area that is not grounded. our neighborhood age and my guess on this house I would plan a remodel that allowed me new plumbing and electrical.

The positive cash flow is often times eaten up by management costs and repairs (new fence, new carpets will be needed, plumbing, lawncare, etc) If we were more aggressive in how we negotiated and more specific with our vision/needs we could have found a property that offered a positive cash flow which would cover expenses and while also creating for us a passive income stream.

I’m looking for a reputable and licensed contractor for a gut rehab including permits and architectural plans, plumbing and electric in Chicago.

Have a plumbing professional put together proposals. 

However, I’m wondering how cautious I’ll need to be with buying homes 100+ years old, or if I should avoid them entirely.The issues I’m most concerned about addressing are:-Knob and tube wiring-Foundation issues-Plumbing, cast iron pipes, galvanized piped-Lead based paint-Asbestos-Old single pane/drafty windows-Old HVAC systems-Roof-Historical preservation rulesI intend to leave the work of fixing most these issues to electricians, plumbers, roofers, etc.

Additionally, if you buy something super cheap, there's a good chance it may need a new roof or plumbing etc. 

Plumbing and wasteline they had to run out there and that was the toughest part.

It's your plumbing.

I’ve had good luck with Cody Allen with Rollins Plumbing.