To start with, decide what you want to make: A Kollossus, an artillery piece or a CD Steam Tank? Looking at the parts, I would go with a CD tank.
To start with, I’d say the wheels are too delicate-looking for anything crafted by a Dwarf: it would just sink into the mud on a battlefield. So maybe try to beef up the wheel rims. Chaos Stars from WoC/CSM plastics to the wheels, like hubcaps Maybe add some kind of dozer blade to the front. Some kind of extra bodywork to cover up the very cylindrical body too, its a dead giveaway.
I like the platform on the back, definitely keep that for crewmen/Sorcerer/Daemonsmith to ride in.
Perhaps consider Ork trukks/Dreds, Defiler, Inquisitor Karamazov’s throne, Penitent Engine, IG Sentinel for bits. Depends how crazy you want to go really.