...and Feruchemists (you'll see more of them later) rely on metal that's worn. So no holding a sword and using it as a steelmind, say.
But isn't that what Sazed did in the Homeland prison? Well, a lock and the bars of his cell, but the principle's the same. Heck, it's not really different then the Lord Ruler's trick or Sazed using the rings stuck in his stomach, and I seem to remember either Sazed or Tindwyl using a metalmind they had swallowed. The books imply that touching a large enough and pure enough piece of metal is sufficient for Feruchemistry.
I would say that access to a trick like that - to use metal that's touched rather than worn, is definately a feat-like/advantage-like ability not in the basic Feruchemist package. Sazed is a pretty adept Feruchemist, after all. Stuff in the stomach is just as close or closer to you than the stuff that's worn, so it's the same to me (speaking purely from a game designer's stance).
I'm pretty sure at some point the Lord Ruler outright banned Terrismen from touching any metal at all, for fear they would use it as a metalmind. It was only gotten rid of because it was impractical.
It says quite clearly that merely touching a metalmind is more than enough to do everything it needs to do. Wearing the stuff is just plain easier as you can wear something and still use your hands. You could use your sword as your metalmind if you wanted, but you risk losing it should a lurcher or coinshot decide to disarm you. Though you also risk such things with any metals on your person most Terrismen don't get involved in fighting often enough for it to matter.
As for the dueling canes, since they are used mostly by nobility I'd assume various fancy designs and jewels would be carved into the wood. The fancier the cane, the more you'd impress.