According to the United States Department of Transportation and the Office of Hazardous Materials Safety, the limit for shipping magnets by air is a magnetic field strength of 0.00525 Gauss measured at 15 feet (4.5 meters) from any point on the outside of the package. There are no restrictions on the shipping of magnetized materials by ground. When in doubt, ship magnets by ground transportation.
Using adhesive tape to capture the metal dust is the best way to clean magnets.
No, once a magnet is fully magnetized (saturated), it cannot be made any stronger.
No, neodymium magnets do not require a keeper for storage like Alnico magnets.