Hey! I like your use of retro Helena Bonham Carter for your character! I'm using Megan Follows from 1985 for Antelope.
For Cordie I can reactivate
Salvatore Howlett for plots with her if you have things in mind, he's always there

. I also have other adults such as
Isla Bowen who can have adult friendly or professional interactions.
For Perdita I have
Violetta DeCroix in the year below her, they likely would have been friends as similar class and house. She is leaving school at the end of may though.
Benedict Hunter is in her year and is a bit of a social butterfly including being quite friendly with his female classmates. He's a very nice boy that she would have shared classes with for a while.
Antelope Grace is also in the year below and a different house so connections become a little looser but she is pathologically sociable and infectiously happy so has few limits who she will befriend. She is smart and likes to help others so if Perdita would accept help from a student the year below for her academic woes, Antelope would gladly assist. Antelope for all her rainbows and sunshine is concerningly drawn to the dark arts as an academic pursuit, feeding her own blood to a plant to see what happens and investigating necrobotany over the summer. So if you want a little dark exploration she is your girl.
For all my students a little bit of magic and mystery wouldn't go amiss so if you have stories you want to play i am up for that.
For Noémie it is probably just
Daesyn Mackenzie who would fit with her. She is working middle class and has a bit of an outsider rep because she's something if a tomboy by victorian standards. She's a cursebreaker so is basically a sanctioned grave robber/tomb raider. But she frequents the lower parts of society for leads and is also fairly fluid with her sexuality when the opportunity presents. Super discreet of course as she has enough problems being a working woman who mostly wears trousers.