General kp build for mages:
15 lvls staff mastery
15 lvls mcrit rate
X lvls mcrit dmg depending on what you need
As you reach end game, you can raise staff mastery to 20 if you choose.
Hero trait depends on you. Most mages go with Crack Shot. If you can cap mcrit dmg and don't need the luck, then by all means get apostle for more matk.
And your title says "tank mages" o-o did you have a question about that or..?