plumbing: fresh water supply lines, could be made of anything, anything other than galvanized or copper has to be replaced, and generally galvanized collects calcium, rust, etc. and becomes clogged over time, so expect to replace it all, if lime, (calcium), iron (rust) or hard water issues exist.
Knob & Tube wiring, bare wiring, crystals, cloth insulated, ungrounded service, and everything since 1900 could abound. Expect to be replacing a lot of wiring and house service itself before that can begin.
Asbestos - most likely on 1930+ rehabs and on the hot water pipes feeding radiators, insulating boilers, and don't assume if forced air furnace that those ducts are fiberglass lined, if prior to the 80's, they're prolly asbestos lined. Lineolum or vinyl floors and their mastic, expect asbestos. Manufactured boards of anykind, expect asbestos. That "mica" type granular insulation anywhere -- is asbestos.
LEAD LEAD LEAD. Lead in the water lines, Lead paint, Lead everywhere. Solid and sheet lead flashing, faucets containing lead, you name it, if its the least bit metal, expect it contains lead or if painted, expect the paint has lead.
Don't plan on gardening anywhere near any structure, as old time termite control and other pesticides most likely permanently contaminate the soil near structures, and the lead paint makes any edibles grown there to surely contain lead. Humans, other animals and plants mistake LEAD for calcium and potasium and suck it up and hold it there permanently, as does your own body (bones, muscle tissue, and the like), so if this bueaty of a home also has you dreaming of vegetable and herb gardens just off the kitchen, plan on TOTAL CONTAINER gardening (or the raised/sealed "square foot gardening" methods) indefinately.
But...the charm and beauty of old time construction...and the careful restoration of same...can bring wonderful results...and a charm that new construction can't beat.
Good Luck to you.