Deep gray and all the other accents in silvery old wood and cream. This will add drama, allow the other elements to bring ion light and set off the concrete wall as a true feature. If you want light instead of drama, then go for a very pale beige stone. It will echo stone colours in both the concrete and rocks...

based on the drawing, the wall where the bed is. HOWEVER, you mentioned that this drawing is not a true depiction of the furniture you will use and the wallpaper. if that is the case, i think the wall paper can work on either wall, it all depends on how busy this wallpaper is and how "plain" the bed is. if you go with a busy wallpaper behind the bed, you may want to keep your bed and bedding on the minimal side so that there is a good visual balance to the overall composition. if you go with snazzier bedroom furniture, then a busy wallpaper may be a bit much and you may want to put it on the other wall or use a textural option to serve as the bed's background rather then another focal point.

Sophisticated start. You could go with black and white photography, architectural pieces, art pieces- anything you love on the wall. Then, add pillows in the colors of the art work. If you want to stay more monochromatic, think in terms of textural interest, such as a shag area rug, pillows with seam detailing, etc.

Hi Jacky, What a great start to your room! Mustard is a really versatile colour and you can do so much with it. To help with what else to use there are a few other things to take into account. What sort of flooring do you have? How much light comes in? How big is the room? What sort of bedding configuration will there be? What will the bedroom be used for - a guest room or for family? Apart from rustic, how you want it to feel - relaxed and calming or fun and edgy for example. Are there any other colours that you have used a lot in the rest of the house? Thinking about all those things can get you heading in the right direction for a whole room look and colour scheme that you will love.