Now you need to prime the interior of the dollhouse with a flat, light colored paint. I suggest you go ahead and paint the ceilings as well.
You need to paint your windows too because they can not be done once the wallpaper is in place. I can not stress how difficult it is to paint these detailed windows. You will find that paint easily clumps along the corners of every tiny mullion decoration.
The best way to do it is to just paint one side and then dab your brush along the corners where the clumps gather. Then do the same for other side. Sand both sides and use a foam brush to dab more paint on each side. Then you can use your finger and rub the windows on each side to finish smoothing the paint.