There is an element of adopting a persona, but most Steampunks aren’t really playing someone different but themselves under different circumstances if that makes sense? The way I see it it’s more a release of the person you feel you really are than putting on a different character. Of course, there’s quite a bit of licence in that. Lots of Steampunks don’t act at all, they just enjoy an opportunity to wear the clothes (outfit) they like. You’ll find many wear lower-key versions of their outfits on a day-to-day basis, the events just provide a chance to wear the full shebang without fear of ridicule. My understanding of Cosplay is that it’s more about taking on a role from a book, comic, game, tv series… than it is creating a persona based on yourself or just wearing the things to like to wear.
There’s a distinct difference between Steampunk and Cosplay, although some Steampunk does involve a degree of roleplay and ‘costume’ (although we call them ‘outfits’). I did an update about the characters featured on the kickstarter yesterday: HERE