Once the flower fades, the flower and stem can be removed. The leaves must remain on the plant until they turn yellow and die. The leaves provide food to build up the bulb and form next year's flower bud. Foliage cut for flower arrangements is taken from several plants, not all from one.
To sand coves, wrap sandpaper around small lengths of clear flexible plastic tubing. Most hardware stores carry this type of tubing. Choose a diameter smaller than the radius of the cove. Slice the tube down its length and slip one edge of the sandpaper into the slit. Then wrap the sandpaper around the tube and hold it tightly.