When I leveled my dk mage I ran 7 light pieces because you don't get the undaunted passive til late in the game. And what I did to level heavy and medium armor up was I have 7 medium or heavy armor pieces with training trait on them and when I turn in each quest I swap to that armor and get the xp from quest turn in to level medium and heavy armor up. (I made 7 light, medium, and heavy with training trait on them at level 1 and made them purple to give more xp bonus to armor leveling and keep them in my bank or whatever and use them again when I level new toons). Also, to make changing gear easier before each quest turn in. I have a macro set up that would automatically switch my armors with a press of a button so I don't have to do it manually. And have another macro to switch back to your normal armor. Was able to get all armors to 50 by around v1-2. I find running 7 light while questing/soloing to be beneficial because you not only get the extra reduce cost in magic but also more spell pen. Also, while leveling I used 5 seducer and 3 torugs with jewelry enchant with spell damage. With the reduce cost from 7 pc light and the seduce 8% reduce cost you should be fine with Mana for each fight/mob pull. When I hit v1 I ran 5 warlock 4 Magnus and 2 torug. That way the jewelry I wear is also part of a set. Also I used the same v1 gear all the way til v14 no need to make another set and waste mats.