Ask Lemmygrad

Signal. There will definitely be people with valid and not-so-valid criticisms of it, but it's a very good tool for organizing. It's low-barrier-to-entry, it is very secure (conjecture notwithstanding), it scales really well, and does chat/text/video. You can have big "general" chats, and many other smaller ones for more specific or spicy reasons. Always make use of the disappearing messages function, as well as the username function.

Outside of Signal, you'll need someone plugged into the "normie" channels like Instagram and Facebook and tiktok etc for public announcements. Certain actions you'll want to announce securely via somewhere like itsgoingdown.