Hi!
Yes, you are correct. No reservations are needed to attend Mass. There is a separate queue for those attending Mass, marked "Mass access only". Entrance still subject to the available capacity inside the cathedral.
You can stay and visit the rest of the main floor of the cathedral after Morning and Afternoon Mass without having a separate time slot. FYI, the Morning Mass during the week and on Saturday don't include the Notre Dame de Paris Choir. Evening Mass runs until closing, so there isn't time to visit the rest of the main floor of the cathedral after Evening Mass (except on Thursday when Notre Dame is open late, until 10:00pm).
Someone else already commented the link to my Reddit post with all the full details, that I do regularly keep updated (thanks, Lynn!), but the bell towers are currently still closed to visitors, but are estimated to open sometime this summer (2025). The exact day is still TBC. Advanced reservations will be required, and there will be an entrance fee (this is no different from how it was before the fire), but no details have been announced yet. I estimate that it will be approximately €15.
(Also! Off-topic, but I just noticed that you're from Hershey. In what feels like a life time ago, I spent a lot of time there. I'm pretty sure I still hold the record for the most number of rides on the Skyrush rollercoaster at Hersheypark, haha)