Because the style is quite modern eclectic, my thought was that a muted cow hide rug could work If you feel a bit more daring - these muted colours would echo the traditional carpet or failing that go for a high sheen textural rug that doesn't compete with the monochrome elegance

I would definitely paint out timber frames, they in themselves become the feature if you don't…..and I would hope you mean a soft grey! To "hide" skirts and arc's (I renovate and sell for a living) I do them the same colour as the walls but in a satin finish…..you could do semi gloss….a water based enamel works best. Make sure you prep them well though, either a good sand to rough up, or something like ESP. I always thought rule of thumb for a feature wall, paper or paint, is the wall opposite the greatest light source, ie. the wall that gets hit with the most natural light. Failing that, I think it would look lovely on the alcove/bay window wall and do the inset of the alcove/bay window in a contrast….say a soft version of the pinkish hues in the paper??? You seem to have some substantial pieces of furniture, and a piano, so doing the other walls would compete and look overbearing to me. Unless you are going the whole Regency style embossed paper/stripes/pattern everywhere…………...

I see wallpapered ceilings a bit in photos. See example. I can't imagine that would be easy to do! An application I did like was wallpaper between dark painted rafters. It was really effective. I don't envy the person who had to do that job. Or anyone who wants to remove it later. In my previous home, every room had been wallpapered sometime in the 80's. All bedrooms, hallway, living room, kitchen, bathroom, toilet. Quite a process to remove! I don't mind wallpaper but I didn't like the ones in that home. I think wallpaper can work really well in homes with a grander scale. High ceilings, architectural trims etc. In smaller homes, a restrained use is more appropriate IMO.

I agree paint may be more versatile - but the right wallpaper on a feature wall with that deer head would be so freaking awesome ! Depending on your colour scheme, if you go with a vintage or art deco pattern, fairly subtle and with a slight texture in it, that'll beautifully offset the deer. And if it's the right choice then you won't want to change it for the next few years anyway. So definitely wallpaper - there's some great 'wall candy' around :-) Good Luck !