I think it is charming the way it is and if you put some big birch branches or something sculptural in there and some contemporary natural wood pieces or primitive art in the living room, it would all blend together. Please don't take out the windows--that will affect the whole face of the building. Rustic and modern is mixed all the time and can look terrific and give the place a little character. I think the Europeans do it particularly well. You could tone down the mortar with a stain. Unless it is in bad shape, repointing is messy and expensive and tough to do well.

Not sure if the large green shrubs are the conifers.... At least they are evergreen, which your mixed hedge won't be and I suspect it will take quite a long time for the mixed hedge to grow and thicken up. I don't know how big your garden is but have you thought about 'blurring' the boundary rather than completely screening? You could put up trellis panels either side of the pretty Wendy house but set them about a foot away from either side, no taller than eaves height, about eighteen inches away from the boundary so they don't look like part of the fence. Paint the panels and Wendy house in a colour that tones with your house. You could even place other matching trellis panels of different heights, in line with the boundary but at different distances from the fence and gaps of a couple of feet between them so they don't make a solid barrier. Next summer you could grow sweetpeas against the trellis panels giving you some quick fix screening and fragrant flowers for the house. I would recommend square trellis rather than the fiddly diamond trellis. Failing that you could try and trim the conifers so they will eventually blend in with the mixed hedge.

I would say possibly no on two fronts - You'll be changing the roof pitch and design. ( I'm no Architect or structural engineer - but I don't see how you're going to achieve the design above without completely re-building the roof ) What your'e describing - and what would work with what you've got is something more like this:- The two extensions being:- Firstly the 'infill' on the second storey to bring it in line with the dormer to the right - but the roofs would look like the above. Secondly the flat roof 3 metre 1 storey extension on the ground floor to facilitate the roof lantern or lanterns. Also, it would depend entirely on how close you are to your neighbours. If they are within 2 metres either side then you can only have a height of 3 metres ( no two storey ). That's my understanding anyway.

Hello, it will be an extension, probably post-war when indoor bathrooms, etc, were starting to be introduced. If it was once used as social housing the extensions were more than likely built at the same time by the council. You could try local authority records to check if this is the case.