I think that the idea is solid, although I would suggest considering giving your wizard and apprentice more gadgets and whirlygigs, and perhaps a big backpack filled with Curious Items of Wondrous Technological Artifice. Perhaps their firearms could be "tricked-out" with multiple barrels, telescopes, etc., in order to represent an array of different spells (shot, flamethrower, a concussion device (for the spell that pushes the enemy back, and so on).
I'm not sure what sort of spells you intend to take, but the possibilities are endless:
Leap - spring boots, or a steam-based jetpack (or perhaps DaVinci inspired wings).
Shield - forcefield generator.
Strength - a clockwork arm frame that increases strength.
Heal - medical kit
Reveal invisible - a souped-up telescope with gears and a crank.
Grenade - a bomb (obviously).