1) "Tabs"
2) Depends on what CAM software you are using. Most 2 1/2D CAM packages have the ability to add tabs to your part. (SheetCAM works well for this)
3) They don't have to be very big to hold the part securely. Make the length equal to the tool diameter and the thickness equal to 1/4 the tool diameter. Use 3 tabs as a minimum. The tabs shown are a lot smaller. This may be due to experience with cutting this particular part. You will find out how small you can make them with experience.