The Pesach night proceedings are commonly called the "Seder" (סדר). This word more generally means "order." What is the first recorded use of the word סדר for this event?
It seems from here for example, question 148 that it is a custom to recite Shir Hashirim after the Seder. It says, According to the Midrash, Shir Hashirim is an allegorical song describing ...
Who is the author or what is the origin of the song commonly found in the haggadah called Echad Mi Yodeya?