I've never had a problem with mana leak or much of anybody. Upgrade the basics for the mage then stick to the specialty like the Clan Leader suggests. Poison water has Poison wave and paralyze and can outlast anyone with enough mana. Burning Hill, the one I won all my badges with, is STUPID strong. 640 damage from one combined bolt. Instant kills most mages.
Pretty fun! But slightly disappointing once you realize each clan has its set of game-breaking that let you breeze through the enemy AI assuming you went with the clan's strengths.
 "Immortal Souls: Dark Crusade"){kind=icon}
 "Book of Mages: The Dark Times"){kind=icon}