Only a few zones were 100, Pocket D was one. Most of the city and hazard zones were 75 post-freedom, Atlas Park included. RWZ, The Hive, and The Abyss were 50.
Unity Rally had 2,600 on Virtue (maxed), and around 4,300 total logged in at the height of the event, but not all of those were there for the rally. I'd estimate around 3,500 - 4,000 who were there for the event.