You'll probably want to use an automated tool to invite them. The thread below has a good roundup of channel management tools. So far I like @openrank Cura but there are several options.

You probably don't want to invite all 7k followers to post. Think of membership like inviting users on stage in an audio space. You might not want to give them the mic unless you're sure they have something interesting to say.

This Notion doc has all the details on the channel changes: warpcast.notion.site/Channels-10a...

warpcast.com/dwr.eth/0xe1...