MC reaction overhearing the heroine talk pulls up 2 flags, 1 he disliked how she talked about her parents being bad with management but still being able to send her at that school, 2 she betrays the hero for money or connections, MC remembered it in that moment and for that who a focused expression.
I just think that if we were made to see that part there is a reason that will be revealed in the coming future.
No idea who the first match opponent is, I'm guesggin that from the little we see is someone Demonio bullied in the past before MC got the body or a male character with a small role but that appears often in the story and CM simply forgot him.
Congratz to the author for making the MILF with a husband look normal and not a sex bomb, MC doesn't have to NTR anyone.