[X] Make it a potluck - everyone can bring something!
This concept might not have been heard of by some of the guests but really this is a good way to have a combination of foods for people to explore.
[X] Cho and Nigel - who seem a bit disconnected from the rest of the group
They at least came even if this party is not their cup of tea and/or close to Shinji, so Shinji should at least play graceful host and attempt to integrate them into the larger group.
[X] Draco Malfoy
Playing Granger is just asking for trouble. And while I can see Shinji playing Iris, I can't help but think that Shinji would love to play Draco here. He can use this as a way to relax and state all the things he would have a hard time saying to Miyuki or other girls since in this case he would be playing the love struck Draco crushing on Iris. RP was supposed to get Shinji to work out his issues, well there you go Shinji. Now go flirt with Amber/Nats under the cover of the sake of playing your character.