Op, I have a Roubaix and here's some things to consider. I doubt that 28mm tires will fit. With a carbon seat post I wouldn't want to hang much extra weight from the saddle. Depending on your weight, lightweight racing wheels may not be the best with extra weight. I have a lightweight steel road bike that I would feel more comfortable with for your intended purpose.

BTW the Roubaix is a very comfortable bike. I love mine!