Plain ceiling white is a good choice for ceilings. I'm a huge Natural White fan but will consider Whisper White next time I'm painting.

Try dulux snowy mountains. Just hope you plan to bring some colour and textured elements into space. With the tiled light floor, the effect might a bit cold.

I favour stone against cedar wood tones. It's a cool neutral and usually contrasts with the warmth of the cedar beautifully. It also creates a neutral backdrop against which you can accessorise and change to your hearts content without needing to repaint. Here's some idea's from Taubmans site.... https://www.taubmans.com.au/homeowners/colours/colour-trends I would probably go platinum or pebble half. Although those colours look heavily pigmented on a chart, against the richness of cedar they would appear very pale but not as stark as a white. It's also quite period correct and easy to live with.

I would not paint that wall. Instead I would install a rectangle huge colourful painting. This will bring interest and texture to the whole room. If you are thinking of going grey, then would it be a feature? Would anyone notice? Your home is quite subdued in the colouring....maybe some colour may pop on that wall instead of more subtle tones.