TS, It's my first day as well!!
After MUCH thought (channeling all my nerves into deciding what to wear, naturally), I am going to wear either a sheath dress and topper OR a pencil and button-down with a cashmere sweater.
I decided to definitely wear a skirt or dress, as after a lot of looking around at blogs and articles I decided skirts and dresses will just look nicer and I want to make a good first impression, as I will be meeting quite a few new people, I suspect!
Good luck! I'm making a change after almost 7 years, and am changing industries. I imagine that after such a long stint it will be both exhilarating and terrifying for a while. You are beautiful, creative and brilliant, though; I'm sure you'll nail it!