I just read about the idea of unlocking perks via challenges, and it sounds great!On the "unlocking hints": Could that be linked to the difficulty level? Eg. on Apprentice they will always show?
Keep in mind, though, that we shouldn't make these things needlessly hard to figure out. I would suggest having some form of hints on every difficulty, though more specific ones for the easy difficulties, because otherwise we'll have a load of players with no clue on how to unlock these perks... and many cries for help on the forum.
The challenge should be completing the challenges themselves, not trying to figure out what the challenges actually are, if you get my meaning.