Hi hols,
There is no set dress code for dinner and the disco - of course if you wish to dress up on NYE then that is entirely up to you.
The hotel is situated some distance from the centre of Paris. However, you can get a taxi into Paris but it could be quite expensive and probably more so on New Years Eve. Your Tour Manager will be able to help with any queries you may have whilst over in Paris.
Kindest regards,
Monty