Okay then, you have tons more experience sewing than I do. :P I just meant that without knowing that, I have no idea if someone wants to "make" a costume by assembling it out of acquired parts, or sew/craft everything themselves.
What will work and what won't ... well, if it fits and you can justify your character wearing it, that's a good start. In terms of "is it steampunk", it's hard to be exclusionary -- steampunk is about creative anachronism, and you could define it as having a Victorian aesthetic but not necessarily, since many steampunks are branching out into costume inspired by other cultures of the 19th century, or timeshifting it earlier into Regency or later into Edwardian.
Ori the Dwarf
Urania, Muse of Astronomy
Random steampunk wardrobe items