(very mild spoilers that will not impact your enjoyment of the show IMO)
I really liked the use of the community theater production of Cabaret in the latter part of Season 5. Dan Levy, who wrote and co-directed the episode that covers Cabaret's opening night, must really know the show (and seen the Sam Mendes version...). Everything that happened, both on stage and off stage, was consistent with the actual stage musical. For example, the opening number on TV was the actual opening number ("Wilkommen," of course). And the backstage dialogue was placed at a point in Cabaret when it could have actually happened.