Twitch users joining channel to attack (screenshot from IRC logs), stalled by Follow-only chat being enabled:
My email notifications from Twitch would indicate that a few of these accounts did follow in expectation they were going to wait out the 10-minute wait time in order to be able to attack the channel once the time had elapsed:
While I do have logs for when they followed through Twitch email follower notifications, I don't have logs on when they unfollowed (thybreeze later refollowed, no new notification was sent, likely due to being in the same day), so I can't be certain what was said during the stream to cause them to back off, however I discussed with this friend over Discord that when I saw the attack coming, I increased the minimum to 1 day. Other things that were stated included the fact that I was considering banning every single account that joined when this group joined (something I'm still not certain I want to do as it's not certain every one was a part of the group, however I would expect otherwise), also bringing up the fact that the last attack resulted in 5 reports to Twitch & 3 to Epic Games, which could have resulted in a ban on iBreezyy's Fortnite license (not that I would expect Epic Games to do anything on offsite activity, I chose to file the complaints regardless to see if anything would come of it).
The Follower-only chat now has a minimum of a half-hour (increased from 10 minutes from the attack 5 days ago), it will continue to increase as I see this continue to happen. The date that I disable this function also got pushed back an additional 5 days (to 4/24/2018).
UPDATE: It was later determined that the original purpose of coming to my channel was not to attack verbally in chat (this only happened the first time on 3/19/2018 as it seems they saw an opportunity to do it without witnesses, not realizing I would Highlight that stream & upload the local recording on my computer to YouTube), but rather to abuse the report function, which I became aware of due to approximately 17 minutes of discussion at the end of one of his streams, which I re-recorded as evidence & used in a couple reports against him, the 2nd report being successful when I used his statement of being "a child" to report his account for being an underage user without adult supervision (being a violation under Twitch's Terms of Service).