Having read through most of your thread, seen that you are in London and that you got the house for approx 100k less than walk in ready alternatives which are 850k, I have to say, given the absolutely extortionate price of materials and tradesmen at the moment, I would avoid it (unless you really can't afford not to), because it sounds like a money pit.
As well as everything mentioned in your previous post you have mentioned roof tiles, gutters, and so forth. It's one thing buying a do-er-upper if you're getting a 25% reduction in price, but you're not, and you're in the most expensive part of the country for tradesmen. The good ones will all be booked for 6, 9 months in advance too.
My cousin, in a pretty crappy part of Kent, is currently charging 75K for a two storey, four metre house extension to be built, for example re: costs - and, as far as I'm aware, that's just for the bricks and mortar (bricks have more than doubled in price in the last 2 years).
If you have oodles of patience and can budget for the unexpected, go for it. But somewhere that's already in bad condition is bound to have other things crop up that you haven't been able to investigate yet.
And no, it's not blinking normal to open every window and every door at a first viewing. That's how a vendor gets to know you're gonna be a PITA as a buyer and might lead to rejection of your offer. Most I ever do is ask to turn on a shower/bath tap to check water pressure.
Have you checked the sold prices on the postcode on the land registry? I always look back ten years to see if any have dropped in value, or risen, and by how much, and if they've risen, how much, on average per year over ten years, so I can think about negative equity scenarios too.
But we are FTBs so I'm far more cautious about negative equity than those who aren't.