Making a giant island a structure

Hey, ive been making datapacks for a while but ive never made a giant structure and i cant find any videos or posts that explain how to do this in a nice way that i can understand.
Im making a superhero datapack and while adding the green arrow, i decided to add Lian Yu (A giant island). Its fairly big and most likely needs 6~ structure blocks just to cover its width and length, I know i need to use jigsaw blocks but i have no idea how. The island is already built i just need help with the structure blocks and implementing it to spawn naturally in oceans.