A lot of elements of Sailor Moon are inspired by japanese mythology and fairy tales. The idea of the Moon Kingdom and Moon Princess comes from the Tale of the Baraboo Cutter. Princess Kaguya, the villain from the second movie is also named after a character in this story. Another character named Princess Kaguya is the villain of an Inuyasha movie (can't remeraber which one)
I remeraber an episode of SM where the monster-of-the-week was a snake-woman haunting a lake. I think it was inspired by the story of Kiyohime.
In Sailor Moon, the weapons of the outer Senshi (the sword, the mirror and the jewel) are based on the three sacred treasures of the Imperial Regalia.