I emailed them and this is the response: "Yes they are, but please have your documentation / certificate with you as you will have to show it when entering the Basilica."  

You can enter at will and no tickets are required. You determine the length of your visit. Enjoy!

Neither a head covering nor a mask is currently required.

The hours vary but yes you can go when there are no services. See their website for hours and to buy a ticket.

Positive

Yes. It is a unique experience. The lights, sound, and the beauty of the church is really something without equal. The description for the event is as follows: "Light unveils the richness of the Notre-Dame Basilica’s heritage and invites us to celebrate its beauty. The experience begins with a path of lights, revealing the Basilica’s wealth of exquisite works. A progressive immersion into a sonically and visually captivating universe guides visitors to the heart of Notre-Dame. Then, light, orchestral music and grandiose architecture combine to create a unique, three-act multimedia spectacle. Allow yourself to be transported by AURA and discover an unexpected, stunning universe presented upon one of the most sublime canvases imaginable: the Notre-Dame Basilica." Do buy your tickets in advance. It does sell out. Lines at the door can be long so maybe plan to buy your tickets early and then come back a show time.

Again Montreal not Paris !

El show de luces y sonido dura aproximadamente 20 min, creo que 40 min extras para la catedral es suficiente, pero depende de los gustos e intereses de cada persona

Every Sunday till noon that’s for sure but for the rest of the week need to check on the website