The 501st approval requirements are listed in black.
The Sith Lord Detachment defines additional, optional levels of costuming excellence. In the page below, items listed under "For level two certification" are recommended features that will greatly improve the quality of the costume. These items are not required for 501st membership, but are highly recommended. Items listed under "For level three certification" are some of the highest level accuracy features for those who strive to be screen accurate. These items are also not required for 501st membership.
Also note that these two additional "certification levels" DO NOT correspond to the Advanced Standards program of the Sith Lord Detachment, and you are encouraged to visit the Sith Lord Detachment Forum for more information.