I think the difficulty is that you have a lot of things to work around you have a feature wall a patio door a window a TV and a fire. Have you considered mounting your TV on the wall (check if it would hold the weight) above the fire that way you have 2 focus points in the same place. Then I think I'd go with 3 seater sofa and 2 chairs instead of a corner sofa. Then you could have the 3 along your feature wall and bring a chair either side into the middle of the room (off the wall) maybe place a small coffee table in the middle to give the illusion of space. Then a mirror on the feature wall. A floor lamp in the corner by the patio door and maybe a low side bored under the window to give the illusion of hight. I think I'd also stick with muted tones but not just whites and creams. There are some lovely sofas with different patterns so maybe you could have a patterned chair and a full colour chair and add cushions. I don't think I've explained the sofa fabric very well so I will try and add some pictures

Difficult to say without knowing your personality and possible acoustic requirements - when you say music room is it for listening to music or playing instruments or both? would you like to continue with this style or are you more eclectic. What you have chosen is very new, smooth, angular and 'masculine' (not saying that's a bad thing) so would suggest making sure you add some texture (thick carpet or rugs), some 'life' (plants with large rounded leaves, something made of wood) and some colour/pattern (books and interesting items on the shelves - although don't rush to fill them, a couple of large art pieces for the walls, a few cushions - for comfort, not dozens) and remember to add a but of fun that doesn't need to 'co-ordinate' (I love the speakers in orange otherwise I'd go for white). A rich brown suede leather sofa would complement but soften the chair. I would also wait until you have the room ready and if you definitely want these pieces wait until they arrive and see how the space looks and feels for a while before buying anything else. Space changes as you put things into it.

Victoria - for some reason it seems wrong to have the back of the sofa smack in the center of the main window - but not so weird the front! I would need a surveyor to work out whether those walls are load bearing - but that could be a possibility. I did consider whether something like that could work.

Sorry super urgent!!! How much gap looks best above this console?? Should the painting be lower than the candle holder or higher? The above are 8" and 6.25" . around 57" from the floor.. or should I lower it slightly to 6" so there's slightly less gap? Guy hanging it soon..Thank you!