Stephen Stanton based the voice of AP-5 on actor Alan Rickman, specifically his performance as Hans Gruber in Die Hard (1988)
AP-5 is named after Rebels producer Athena Yvette Portillo. According to Starwars.com, the number 5 in the droid's name refers to Portillo's height of five feet tall. The design of the droid is based on the 'Death Star Droid' first seen in the original Star Wars film, specifically on early sketches by Ralph McQuarrie.
At around 10 minutes you can see alien writing. It is in Aurebesh, and means "This side up". The text is mirrored.
This episode features music based on the market chase scene from Raiders of the Lost Ark.