We were on the May 22nd tour. There were just 24 of us on this Classic sized tour. We weren't scheduled to do so but Tauck generously took us to the Louvre after hours.
If you plan to go to the Opera Guarnier opt for the English speaking morning tour. You will be able to sit in the auditorium and possibly see a lone dancer like we did. Our guide told us that if there is a performance the auditorium is closed to the tours in the afternoon because of dress rehearsals.
We don't like being pinned down to a specific time slot. So, against all advice we did not get museum reservations. We had no problem walking in. the only exception was St Chapelle. We had to wait about a half hour. I understand, though, that in the late afternoons you can usually just walk in. This is a beautiful church. If interested, you can see how beautiful this church is in a show we made of the trip: 
https://youtu.be/efFq18C4T34
