The name of the song is "The Skye Boat Song", a late-19th-century Scottish song that has been covered by many popular musicians and used in various television shows, including the theme song for Outlander (2014).
The character of Walt is clearly young, yet has white strands of hair. This is likely a result of his trauma as a child from losing his sister.
The Witch House exterior is modeled on the Turner-Ingersoll Mansion, an actual house in Salem, Massachusetts. This house was also the setting of Nathaniel Hawthorne's novel "The House of the Seven Gables".
Masters of Horror (2005), another horror anthology series, also had an episode with this title based on the same story by H.P. Lovecraft. However, the plot of the two shows differ quite a bit from each other.
The name Epperley is from "Apperly", which means apple wood or clearing. One meaning of the name Walter is "army". Both names are fitting for the characters in this episode, in which a man named Walter is fighting to rescue his sister from a spiritual forest or wood.