Re: The mandolin goes... steampunk?
You might want to add some rags and comic/parlor songs from the late Victorian Era as well to your repertoire. If you don't necessarily want to stick to time-period songs, you may want to look at somebody like Jonathan Coulton for mad scientist and monster-themed songs (Paul and Storm's "Live" is pretty good re reanimation of corpses). As for costume, that's up to you. I'd look around online to see what some Steampunk costumes look like. Maybe you should attach pistons to your mandolin?
"When I heard what Socrates had done on the lyre, I wished indeed even [I had done] that...but certainly I labored hard in letters!" - Cicero, "Cato the Elder on Old Age"
Mastercraft MSF400 F-style mandolin
Late 19th Century Ferrari(?) Bowlback
No-name, early 20th Century British Mandoline-Banjo
1960s Harmony Baritone Ukelele
The Magic Fluke Flea Soprano Ukelele (in 5ths!)
1910 German Stradivarius 1717 copy, unknown maker
1890(?) German Stradivarius 1725 copy, G.A. Pfreztschner, maker