Hi Frank! Welcome to the forum!!!!!
Modifications over winter? Hmmmmm. Great question. If you had a C5, I would have more answers but I don't know too much about what to modify on a C6. For the first year, I would probably look at different body modifications. Looking at maybe adding a rear spoiler, or chin spoiler, side skirt if any of those interest you. Basically cosmetic upgrades. Next summer, take the car out and find out what it's lacking. Maybe new rims/tires, brakes, suspension, headers/cam, etc.
Now that I think about it, If you are thinking performance stuff. A great place to start is headers and a cat back exhaust. There are a lot of fans of Corsa on this site but I am a Borla fan, or GHL or Akrapovic. The cat back does't add much for hp but adds a lot to the sound. The header however, actually do add to the hp.