Magic
The practice of magic is a dying art. Magicians (the general populace does not differentiate between Wizards and Sorcerers) are seen as archaic relics of a time long past. In an age of clockworks and steamworks, most find it simpler to use mechanical devices than dedicate themselves to the arduous study and research necessary to wield magic.
Wizards are "encouraged" to register with the Empire, though Hedge Wizards and the like who keep their heads down and stay away from the large cities can easily slip through the cracks. The Empire does have Magicians in its employ.
The Church's position on magic is much the same; it, too, claims a few Magicians among their ranks. However, the Church does frown upon Summoning/Binding type magics - it smacks of "deals with the devil."
Barbarians
Treat Barbarians as "berzerking warriors." The cultural connotations of the Barbarian class do not exist in this setting - they could be anything from a warrior with an attitude problem to an uneducated street thug who flies into violent rages at the slightest provocation. And they do not suffer from illiteracy.
Craft: Clockwork, Craft: Steamwork, and Demolitions
The Craft: Clockwork allows the character to create mechanical devices powered by an external source - typically, by "winding up." Examples of these items would include pocketwatches, childrens' toys, etc.
Craft: Steamworks is used in the manufacturing of steam engines, which are most often used to power massive clockworks, ranging from trains and hydraulic elevators to - hypothetically - war machines.
Any class can take Demolitions, though a character with this skill should explain how they received the initial training - most often this would be from serving in the Imperial Army, though there are certainly other ways the character could come by the knowledge. This skill does not cover the creation of Black Powder itself, but rather the best ways to use it - how to blow up bridges, create complex bombs, and the like.
Edit: Demolitions would also cover the use of artillery and cannonades.