Hi senba, Great suggestions above! Yes, use the wallpaper background... but keep it really,really light blue. It will keep the room homogenous and will retain the softness of your paper. That is going to be a very pretty, very fun room when complete.... please post a picture! Elizabeth Cabell, ASID, CID

If you want to highlight the staircase wall then your could use earthy colours such as a yellow ochre! The wall could be enhanced even more by using suitable frames and making a good collage composition for all the photos that you have (I can see many lying on the dining table). This colour would match well with wooden furnitures

Reclaimed wood ,use pallets you could take apart and nail them up .Could be free if you look on Craig's list for free pallets

Give search for home theatre door in houzz and it will give you a few ideas. But finally what you have to think or take help from interior designer is about the theme of your home as this door should also get aligned with your house theme. In general having hallway as part of home theatre is not advised so if you can change it, it would be better. But if you can't then at least install auto closure.