For D1 a 1N54xx should work. It is rated at 3 amps.
http://www.onsemi.com/pub_link/Collateral/1N5400-D.PDF
Or if you do have to go with a 5 amp circuit then a MR75x at 6 amp rating.
http://www.onsemi.com/pub_link/Collateral/MR750-D.PDF

For the zener... That is to protect the regulator from a higher voltage than it is designed to handle on the input. If you regulator can handle say 35 volts then a 22 volt zener would work, but what are the chances of the voltage going over 35 in a car? Z1 may not be needed. IMO