Re: Help me craft a mythos!
what i've had fun doing with my campaign's mythology is to never give a 100% objective account. everything is slanted heavily by the views of the culture or individual relaying the information whether it be in a book or from a Grand Green Wyrm with really awful diplomacy. :D Not entirely sure if that's helpful to you, or if your PC's will be delving really deeply into your mythos, but as in real life they should take the stories with a grain of salt.
perhaps a really trusted source only knows some fairy tale with %20 fact, and that premise is bought wholeheartedly, but a villain, or less trusted source provides the remaining huge chunk of truth. ("Obi-Wan never told you what happened to your father") That will generate such massive catharsis that your players will be floored and quite possibly all shook up.