Then I’d fetch all followers, update via webhooks and periodically refresh the stack, if my cache of a follower is stale (last checked in 24 hours) I might consider fetching their follow status, but that mean latency in the fetch delaying the command, assuming you make the fetch block the command rather than background job it.
Latency would be worsened on the bulk fetch you propose. So on a large channel, such a thing is probably not worth the CPU cycles, which again it isn’t at all if the channel is in followers only mode.
Course this means moving the check to the background so lookup latency isn’t an issue.
You should always cooldown (in my opinion) regardless of follow state, as otherwise you might get close to your send limit even as a mod or verified bo, and then your bot gets kicked out of chat.