This is where webhooks can come in. If you have a complete cache you would already know which of the influx of people in chat are followers, and if those who aren’t following but then decide to follow that will fire a notification to your webhook subscription so you will know of new followers moments after they happen without needing to query the API. The only time webhooks will use up your rate limit is for the initial subscription, but the max lease time is 10 days so even with hundreds of thousands of channels, if you stagger subscription renewal it has a minimal impact on your rate-limit.