1. Yes, the 3 S's in “CONFESSSION” is intentional. Kouhei elongated the word out of surprize.
2. I intentionally didn't tag this with a volume number because A. That's factually accurate. It's not included in Vol. 2. but also B. While people sometimes tag such chapters anyway, putting it in between Chapters 12 and 13 totally interrupts the flow, so where it is now works best IMO.
3. My current plan is to finish up my work on the main series with Ch. 19.7 and then move on to the many X extras, so follow
that page if you're intrested!