I would draft up a "framework" for some archetypes I was expecting to see in my game. The whole "do whatever you want" always ends in disaster. Players don't need a wide open field, they need the ability to customize and personalize a character to fit what they want to play.
I would do something like this;
1) The plucky witch - wants to uncover the secrets of witchcraft to empower themselves against the unknown.
2) The reluctant adept - learned to channel energies into their martial discipline, but has reservations about their new-found power.
3) The magical genius - curious and ever reaching for more knowledge, seeks the secrets of the magical-verse.
4) The troubled sorcerer - infused and patronized by an otherworldly power, works toward controlling impulses and influences of this strange benefactor.
5) The repentant monster - this human-looking creature from the "other side" has shed their alien ways seeking redemption for past deeds.
6) The inspired rogue - magic and mystery are keys to unlocking the hidden fortunes of the world, both tangible and not.
Then, you can design a campaign, motivations, hooks, around these archetypes.
I personally am really digging Unisystem these days; a nice compromise between crunch and rules-light. Traditional approach. Look at Withcraft (classic) and Ghosts of Albion (cinematic) for ideas.