Simple really though tedious. Note the x,y,z size of the object then for those objects you don't want visible set the size to 0. 1 frame before you want it to appear set a keyframe then go to the next frame and set the size of the object and a keyframe. Do this for each object. To make objects disappear reverse the above. Another way is to put the objects out of the camarea frame then set a keyframe before it's to appear, advance frame, move it and set another keyframe.