You're ready to create a transition from the sketch of the room to the high-res photograph of the room. All the layers are in place, and it's just a matter of adding four well-placed keyframes:
Add a 100% Opacity keyframe to the Img_14bigSketch1 layer at time 2;00 in the Master Timeline. Go to time 3;00, and change the Opacity value to 0%.
Add a 100% Opacity keyframe to the Img_14bigSketch2 layer at time 3;00. Go to time 4;00, and change the Opacity value to 0%.
Go to time 5;00 so you can see the Img_14bigSketch3 layer in the Composition window.
To keep FillMovie from just popping on the screen, add a 0% Opacity keyframe to the layer at time 0;00, and then change the Opacity value to 100% at time 1;00.
To fade in the Background layer, add a 0% Opacity keyframe at time 5;00; then, go to 6;00 and change the value to 100%.