when i've run it magic is mostly discovered by doing work for existing magic users, or learning it from any of the grimoires found. there is also the possibility of learning some magic from one of the demon-faced coins.
i've heard some tables leave the spell lists accessible to the players so they are instead actively seeking the ingredients rather the knowledge of the spells. personally i prefer having it all hidden, but you know your table best.
similarly, i'd shy away from starting with knowledge of magic but as above - you know your table best.