The group is at a critical point now, having ~100 Whatsapp members. From what I've seen this creates a chilling effect where you inevitably end up with cliques and social cooling.
No new members will feel like they can actually send a message into a 100+ person group, while the old guard starts to use it as a notification board, rather than a real chat.
Eventually, newer members will feel too far behind the current discussions, and too socially exhausting to show up to meetups. I've seen these eventually get to 400+ members, many of whom don't live in the city anymore.
The best group I've ever been part of had a simple rule that worked amazingly: If you don't show up to an event at least once a month, you were removed from the whatsapp group. It keeps the group small, and comfortable, and it never felt intrusive to send a quick "Whats everyone up to today?" into the group chat.