I would not get a room at the airport. A real waste of money, and eventually time as you still have to get into the city.

Every hotel I have ever stayed at will check or otherwise watch bags if your room is not ready. I would do that, then go around and see some sites. What day of the week will you arrive? There are open air markets that are inteesting and not too demanding if you are not planning to purchase.

To answer your question, there are visits allowed at the opera. Here's info on Garnier, if that's the one you meant (there are two):

http://visitepalaisgarnier.fr/en

Make sure you know where your hotel is, as some Paris hotels use names like Opera and Eiffel even if they are not close to the landmarks so used.