The idea sounds interesting, but I'm left to wonder how it might play out in-game. What I mean is that, with there being so few populated settlements in your Rivets campaign setting it seems likely that such a underworld-centered group as the Troupe party would have to pretty much remain in the criminal underbelly of Trenchtown to remain effective. I can't imagine there's much political intrigue, covert infiltration and assassination going on out in the wilds. That's all fine in and of itself, but it pretty limits the need to travel around by airship. Likewise, if you prefer a roleplay-centered campaign with the the PCs playing the part of covert operatives it seems unlikely that we'll have the need or the means to use steam-powered constructs and armor ourselves. Even the use of firearms amongst the party would likely be curtailed due to their being loud and rather crass for a Troupe of covert operatives.
Maybe I'm reading your intention wrong, but so far it seems that we'd end up playing a local group of underworld mercenaries posing as performers of some sort with the steam-punk aspects of the campaign being largely in the background. There's nothing wrong with that concept; I'm just curious to know if it's accurate. Also, would PC choices be limited to human, dwarf, gnome, goblin and elven slaves? Are their any other PC race options in Trenchtown? Just curious.