I'm not sure blue is the way to go. I think introducing a fifth colour will work. You currently have the sea grass sofa, grey chairs, white table, brown floor. I'd go with the grey or the sea grass for continuity. The living room has two views - not sure if one's old and one's newly decorated. The first is the straight view through the door in to what looks like a hallway and appears grey like the walls in the dining room:- The other looks like another room straight through, but the doorway looks 'amended', so not sure if you were trying out different colours or the view just appears a little weird. Anyway, it doesn't matter, i'd stick with the grey, sea grass and white. I'd also put the T.V on something higher as currently it's quite low down. The T.V could also do with being a bit larger, and I'd move the lamp to behind the sofa otherwise it will glare in front of you and impede t.v viewing.

That looks like Anaglypta wallpaper which is usually painted over. Painted wallpaper is quite an effort to remove but if you hire a wallpaper stripper it will make it easier.

This guide may help as it may be possible just to repair the plaster. It is more expensive to have lime plastering done (it seems a bit of a lost skill and the plaster is dear) but there may be economies of scale if several rooms need doing so they may do one day a week and come back a week later when that coat is dry. If that particular wall is damp you will find the paper will just peel off off tbh. We found damp in a room this year and wallpaper, cross lining and lining paper all came off in ine go. On a positive you do have lime plaster, most of ours has been covered with gypsum which is a whole other issue, so any damp should be drying out https://www.realhomes.com/advice/plaster-in-old-homes

Congratulations on your new home! How exciting! We think the paint colours you have selected sound lovely and a great place to start. The previous owners have placed wallpaper on opposite walls which has the effect of making the staircase look far more narrow than it actually is. I think it would look better to have the same treatment (paint / wallpaper) on all of the walls instead to open it up further. We would love to help you if you need some more in-depth advice with our affordable online interior design packages. https://www.thelivinghouse.co.uk/ - Becky