Cog Hauler works and I think having multiple options for how it could be run would be really nice. There were a number of different armaments when they only had 8 steamtanks, with Ironweld I would imagine there are 100s if not 1000s spread across the realms and innovating new iterations would be very common.
The Dual Pistol mixed with Repeater handguns and CCWs is what my main infantry look like.
I love the Ironsworn, it's a great idea and a beautiful model.
I think your push to move this away from the Empire is exactly what needs to be done. Leave the Freeguild to keep that aesthetic. As I built more and more of the Ironsides a used less of the pummelled helms and more of the sculpted shape helms. I think if there was more option for non-Empire humans i would have used them. A think the mid tier infantry should be all plate, beards and engineers aprons.
I think cawdor is the perfect option for the lower tier infantry. Weld Labourers used as Sappers, menials and Chaff. As I mentioned in the sigmar group I think a version of these with massive metal Pavise would be good. Every artillery train tends to build up earthworks and defence around itself but this is hard to represent on the table table without a custom set of terrain. But what if one of the units became the artillerys defences? It could be a dual kit, one more for hanging around the artillery to replace it's crew and one to become a semi mobile defence line.
The Cogfort has a long way to go, I have a basic structure and have started the surface work but the legs need reinforced corner and I need some sort of relief or etch brass for the front. Very much work in progress. I think here needs to be behemoth versions of this as well as the terrain. Massive multiple weapon keeps that fit the description in Iron and Oak. I will use mine as an Ironclad on the table.
