Minecraft wiki entry for Turtle_farming, associated text: A chest to collect the scutes at the end of the line of hoppers
An extra hoppers may be used to position the chest outside the farm
To avoid using an extra hopper, the chest can be put right inside the side wall with a glass block above it, because chests can be opened with a transparent block above
Fencing or barriers all around the farm
Lighting to prevent mobs from spawning in the farm