Camagnolo don't make bikes, they make bike parts, like gears and brakes.
Many Tour de France winners have won on Campagnolo-equipped bikes. There have been thirty winners on Campagnolo-equipped bikes. The most recent was in 2006, Oscar Pereiro won.
Yes, the bikes on the tour de France have brakes on each wheel.
No. They use regular road bikes and TT(time trial) bikes.
The winners keep them
rookie winners of the tour de France
See attached link from the official Tour de France website.
rookie winners of the tour de france
belgium
They're the same size as regular drop bar road bikes.
Multi-geared, drop bar road bikes and TT (time trial) bikes.
hotel de crillon
Drop bar road racing bikes.
These days, as much carbon fiber as possible.