I've renovated four early Edwardian flats (purpose-built, so agents might call them maisonettes) and a Victorian 2-bed. Similar issues with them all. The Edwardian ones had better proportions, bigger spaces and much more daylight - Victorian rooms tend to need knocking through to make them lighter, unless you're looking at a mansion or something.
Energy-efficient sash window replacements are incredibly expensive, so I put in new double-glazed windows or standard secondary glazing. Floorboards were all nice, but full of gaps - sanding them also means extensive filling, which is a horrible job. I restored a few, but mostly laid new wooden floors on top of the old ones. Sound baffling was quite good, and putting down an extra floor improves it (if you're very noisy you can put insulation down while you're at it.) Keep the skirting boards if you can, they're fatter and nicer than new ones. None of your doors, windows or angles will be straight; I used professionals to fit kitchen units, as they always need detailed adjustment.
I started off being precious about the original cornices & ceiling roses, but by the last two I was buying new plaster ones. They're just as good, and it's easier to pull off & replace than to restore (doesn't apply if yours is an architectural masterpiece, of course, you'd better hone your skills!) I also took out the tiny fireplaces and turned the holes into cupboards; decent-sized fireplaces are nice to keep. You can cap off the chimneys and put bafflers inside, to minimise draughts and things falling down them.
Stripping the walls was invariably hilarious and unhealthy! Some properties had up to THIRTY different layers of wallpaper & paint; it's like time travel! The wall cavities are filled with a vile horsehair & plaster mix, which has collected large amounts of rubble along with debris from small animals and assorted live creatures. I wish I'd put up with wearing a mask, as it's given me long-term sinus problems (and worms.) The stuff falls out even if you just strip the walls. Knocking them down is beyond filthy. You will probably need to strip out much of the plumbing & re-do it, and I had to replace all the wiring in three of them - more time travel!
Lovely details, like hallway tiles and fireplace surrounds, are well worth keeping and most properties still have the stained glass in the front doors. Unless you're going to extreme lengths, you can just patch any broken tiles with filler and paint.
A friend of mine bought a large, neglected Victorian house and discovered amazing panelling behind the plasterboard walls - both carved wood and intricate plasterwork. She also found the ceiling plasterwork was all hand-made, with the detail clogged up by paint. It was a mixed blessing. Took six years to restore, but was gorgeous by the time she finished!
Oh, and watch out for lovely mature trees. Make your surveyor check that the roots haven't undermined the foundations or broken through the waste outlet.