I've got all the other classes, all my buildings are lvl 3 but the alchemist, just finished Doubledoom's quest, and now I'm looking at the long list of quests, wondering which are actually worth doing.
I've got the big list of unlikely heroes quests, Ice and Fury, The hard dungeon quests (beat x with all the classes in building y) in each direction, as well as Halflings, Ho!
Considering how small all the rewards are for the effort involved, I'd rather focus on doing what it takes to get the monster classes, but the wiki is mute on how to go about doing this.