I just kept one character in the camp and never used. Then when I reached lvl 12 took him into group, leveled into all classes and got the achievement...
Wouldnt it suffice to just pick any character, pay 100 gold to reset them, and then level up accordingly ?
Resetting invalidates the achievement, but as noted you can leave someone unleveled in camp and once you reach 12 go back to camp, recruit the toon and then level it up through all 12 diff classes.
But there's no pride in that.
