Twitch chat doesn’t show new follows, so there’s no reason for Twitch to send those events over TMI.
The API is cached, requesting the same endpoint with the same params more frequently than once a minute is excessive, and can actually lead to bad responses.
As for the best way to handle this, you could use webhooks https://dev.twitch.tv/docs/api/webhooks-guide and subscribe to the follows topic and get a notification each new follow (it’ll send a notification regardless of if the user had previously followed, so it’s still up to you to detect and handle a user spamming follow/unfollow)