This was so totally wonderful in so many ways. I loved your carelessly casual Dumbledore who doesn't check what his spell does, Filch who eagerly accepts the bounty that is foisted on him and does everything he can to keep it and poor Severus who doesn't have a good option with Dumbledore and no experience with someone treating him well... this was just 'note on' in all the characterizations.
I enjoyed every minute thoroughly. Thanks so much for sharing this gem!