I'm another to say you're being hopelessly optimistic in your assessment if you are intending to fix everything to a modern decent standard. Most people just put up with the 'quirks'. lots of things you didn't mention like the flat roof on the bay window and it looks like that extension pre dates the local planning records (back to 1990) so that could be a crock of shit. When that back wall was taken out, is it structurally sound enough to knock through the remaining wall? Invasive investig