To be honest Beezerk, as it is I see a major refurb coming on. Unfortunately when the house was built in the 50’s it was state of the art. Roll that on 70 years and utility rooms, offices, extra parking required are now seen as the norm. They were never factored in Because they never had to be. Looking at your floor plans remind me of mIssis Ts grannies old house. The two rooms you have as dining and lounge, back in the olden days they had an everyday room and a “best room”. Only usually used on a Sunday, Christmas and special occasions. Over the sands of time, A previous owner has chosen a lounge and a dining room and that seems to of stuck. Worked in the past but is it ideal now. I think not.
Me, the downstairs cupboard would be gone, if the dining room stays as it is I would open up the dining area into the kitchen, as in knock down the wall and have a brekkie bar there. I would take out the dining room window and get some patio doors in there, bang in a good bit more light With access to the patio. With that you make the decision as to whether you have your dining room open to the kitchen or you have the lounge into the kitchen and then create a “ Snug” where the lounge now is and incorporate a work area for Missis B And the dining area.
One of the things about a dining room, they’re brilliant when entertaining, but unfortunately more and more folk eat their dinners on a tray in front of the box. So a large room becomes dormant for most of the year. So can that space be better used.
All the other things re electrics, Boiler, plumbing etc are secondary to what you want and decide to do. They are all do able but they have to fit around what you see long term Re knocking downstairs about.
One last thing, where the in laws live, there is nine avenues of terraced housing built over 100 years ago for the local pit. If you imagine the Lavvy was at the bottom of the back yard. Now there is none as they are incorporated in the house. Every house has been knocked about. Have you any neighbours who have been through the same process that your looking at doing that you could have a look at for ideas. But also problems they encountered. ?