Brigid is one of the pagan goddesses of pre-Christian Ireland who is associated with the spring, fertility, healing, poetry, and smithcraft. She is also considered to be the goddess of all things "elevated", such as wisdom, excellence, and perfection.
Honda explains to the undercover Legends the special filming method he's using to make his film with a miniature set and special shooting angles set up to make the city look huge despite being on a much smaller scale. It's a nod to tokusatsu -- literally "special filming" -- the term for a genre that makes heavy use of special effects. One of the most common techniques in tokusatsu is suitmation technology, literally someone in a monster suit moving through scale model scenery to give an impression of large size.
When the Legends pay Honda a visit, they claim to work for K&G Pictures, a Hollywood movie studio. This makes the second time the fictional studio has been mentioned on Legends. The first was in Helen Hunt (2017) as the studio that was engulfed in an all-out war with Warner Bros. over Helen of Troy.
Historically, Kaupe is a malevolent spirit from Hawaiian folklore that calls out at night and lures people to their death.
In reality, Ishiro Honda used a giant octopus as a secondary monster in two of his films: "King Kong vs. Godzilla" and "War of the Gargantuas".