The head gear only protects the upper portion of the face so the eye and nose areas are a target for blows. Chances of getting eye and/or nose injuries are therefore about the same as when a boxer is fighting without a head gear.
One punch can put you in a wheel chair for life.... (Or worse)
Realistically, the amateur sport is well governed, with strict rules in place. For example: The referee won't permit a boxer to take a prolonged beating etc..
Boxing is a contact sport and it only takes 1 punch to break your nose.
Not very likely. Don't worry you'll be fine just protect yourself.
Unlikely, but does happen.
What are the chances of broken nose or injured eye in competition being that you where open face ?