OP, get photos and guarantees about the insulation and the damp-proofing. The guarantees will only be so long. You'll need photographic evidence of the underfloor insulation to be sure it's in there. It's an easy one for vendors to lie about. I know this because when I was doing EPC householders lied about insulation all the time.
You realise that with your north-facing garden there'll be little sun on that patio?
The fake radiators may be as good as they get for cast iron rads in that style, but they won't be as efficient as a modern radiator.
You have to ask why they haven't invested in decent double glazing and why they run a dehumidifier. It may be that the house needs to be draughty to deal with the damp. It's actually against regulations for them to be advertising it without a current EPC. These are little red flags.
I think it's an attractive building that they've gussied up to look stylish but it will be a high-maintenance expensive house to run. And how will your family cope with
the small living room and the lack of storage?
You'll be buying a house that a lot of purchasers with £600k wouldn't bother looking at. No private, secure parking. No garage for storage. Cars passing within a couple of feet of your front windows/ door. Built into a hill with all the damp issues involved. North-facing garden. It's not clear whether everything for or from the garden will have to go through the house or whether there's side access.
Not saying don't do it. Saying this is a difficult-to-sell house which you'll be buying at the peak of a boom. If for any reason you need to sell in the next five years you may take a major hit on it because most purchasers wouldn't consider it.