Most of my projects are anime first because I have such a small pool of anime that I like editing from. Or idea -> anime(s) -> song. Like one day I'll just get a really stupid storyline idea then search for anime and songs for hours to see if it would work out or not. If I can't find scenes I'll drop it (or cry and alter the story). I only start song first if I hear something on the radio and get really inspired to edit it.