The opening credits are a mixture of scenes from bat mitzvahs and 1968 Documentary 'The Queen'. Both are used to represent the change the main character is experiencing. The credits end with the date stamp January 1st 1994, the year frequently flashed back to in the show as the start of Maura's journey to stop appearing like a man.
Actress Gillian Vigman appeared as Tammy Cashman in the original release of the pilot but was due to give birth during series filming (the pilot was produced earlier as a standalone), so was replaced by Melora Hardin. For continuity they re-shot Vigman's scenes, replacing her with Hardin, and swapped the scenes in the pilot (removing the original pilot from all official distributors) so it now appears as if Hardin had been cast and shot from Day 1.
Gaby Hoffmann had her part written for her after Joey Soloway saw her performance in an episode of Louie (2010).
This is not the first time Jeffrey Tambor has played a man dressed as a woman. He portrayed a transvestite judge in an episode of Hill Street Blues (1981).