Advance tickets

Tickets for Musée d'Orsay should be booked in advance although not required if you're willing to wait in line.

Wax museum - do you mean Musée Grevin? If so, you do not have to book in advance.

The Cathedral of Notre Dame does not require pre booking although they do offer a limited number of timed tickets 2 days in advance. The line for those without a timed ticket moves fairly well, perhaps up to a 20 minute wait. There is no charge to visit Notre Dame. Try to arrive early morning before the cathedral becomes overcrowded.

If you want to climb the Towers of Notre Dame you must purchase a timed ticket. Unfortunately, the website to purchase these tickets is currently down.

Thanks for the good info!

sherryjb,
Re Notre Dame, be aware that there are times when the cathedral may not be open for tourists because of a special service there. And, of course, times when services are being held may have a small impact on what you see there and where you can wander.

Reservations for the Orsay become mandatory on 10 March:

https://billetterie.musee-orsay.fr/

You do not need tickets for Notre Dame unless you want to climb the bell tower:

https://www.tours-notre-dame-de-paris.fr/visiter/informations-pratiques