@David Coughlin Old homes are great to cut your teeth on, given you have enough liquidity and go in knowing extra repairs can happen. Prior to purchase you need to set yourself up for success: a great 3rd party inspector that is no-nonsense, a local agent that knows your type of home and area _very_ well, feedback from other owner/investors with similar homes (i.e. what to look for) and contractors who specifically work on old homes and know their nuances. At the end of the day there's only so much you can do and I can't understate how valuable local knowledge is. Below are tasks I encountered, outside of renovations, that incurred extra costs and whether or not I could do them myself. YMMV (your mileage may vary)
Fixable alone: boiler maintenance and steam system rebalancing, minor lead paint sealing, plaster patching (even very large ones), thermostat installation, insulate flooring and rim joists, painting, floor repair, skim coating walls, installing thresholds, weatherproofing, installing/refinishing door and cabinet hardware, adjuster gutter drainage
Needed professionals: sewage main unclogging ($), knob and tube disconnection+removal ($$), flooring ($$), adding joists for structural support within walls ($$), replacement and removal of old brass/cast iron plumbing where necessary ($$$), new gas line for laundry and lines for appliances ($), wall demo + replacement ($$$), steam line moving and radiator repair ($$), gutters ($$)
$ - hundreds, $$ - thousands, $$$ 5K-10K, $$$$ - tens of thousands
Hope this helps, best of luck with the old home!