I believe it is in episode #234, but it wasn’t dicussed in detail. Just one of the cast threw his idea out there, followed by small discussion about having seperate names for the Great Spirit (Ekimu) and the island (Mata Nui) I think.
I also have some idea about source of Guurahk’s power. His pride was destroyed when he was rejected from the Toa stone ceremony, so he use his power to reduce everyone else’s hopes and dreams to dust (Disintegration).