Mandamouse, that house is looking really good! I love the shapes you've made with the exterior.
I haven't done much steampunk in the sims, and it'll depend on which expansions/packs/store content you've got, but gears or wheels on items or as decoration can help make it less Victorian. Or even items that can be recoloured to look like gears or wheels (I've had some luck with the fire hose decoration, which I think came with Ambitions. It's nice and round and has more than one colourable area to work with).
If your sims have access to the inventing workbench or sculpting station, you could use the gizmos and sculptures as well. I think the inventing gadgets might be available in buydebug, but the sculpting objects have to be created in game. Play around with it, like using move objects to merge the static testers with table legs to create a 'magnetronic' desk, that sort of idea. Also, there's lists of what can be sculpted in each material - it's random chance what the sim makes at first, but a set of chairs out of wood or clay or metal might look nifty.
Personally, my idea of steampunk is sort of Wild Wild West-ish; a sparsely populated late Victorian frontier where mad geniuses tame steam to their bidding. Lots of sun baked woods and dust and cast iron and brass, with faded oriental carpets and tasseled lamps in the background. The luxuries and fashions have to be imported, which means they're rare, worn out, or a home-made version which isn't quite the same. So for example, I'd take those great wallpapers, but use a wood or wood panelling instead of the light coloured paint for the trims, to try and scruffy them up a bit. But that's just my personal interpretation of the genre - yours might be a coal-fog drenched London where everyone dreams of escaping the murk with airships.
And if you feel like you need more items to work with outside of the Victorian style, and you've got World Adventures, consider if your version of the steampunk world travels. Maybe they're just beginning to explore some Egyptian ruins, or have opened trade relations with the Far East. A couple of ancient relics in the library, or a fortune cookie machine in the study/invention laboratory, could be an interesting touch. Whatever feels right to you, have fun filling up the rooms with rugs, wall art, sculptures, candles, towels, plants, even outdoor rocks brought inside if it works!
Just be sure to post plenty of picture when you're done with the house!
