Quick comment because A: I fail at many things, including public profiles for my characters and time management, because I was going to finish that up this week but got super distracted with actually playing. And B: because I don't have much time at the moment, but we can e-mail or talk on AIM later. ANYWAY.
Cameron Ayers: 5th year Ravenclaw, future co-Beater, gloomy little raincloud, also in Duelling Club, possibly Ronnie's soul-mate just a little bit. He's VERY into Divination, though, and considers it his most important class. I'd say it's likely they already know one another and if they're friends, Ronnie might be the only one who knows he's interested in trying out for Quidditch this year.
Nora McLaggen: 4th year Gryffindor, total ditz who is way more interested in her hair than she is in learning, also in Broom Racing, also not interested in cute boys but actually is a lesbian even though she's not self-aware or introspective enough to know that yet, thinks being popular is the most important thing ever. Mortal enemies?
Keziah Smith: 7th year Hufflepuff, yes Hufflepuff but the child of a Smith and a Parkinson so she can still be a raging bitch on occasion, sells Quidditch memorabelia/luxury items/is a pawn broker so you can sell her your stuff if you need some quick cash. There's not a lot of overlap but they're all trapped in the same castle and they've got the journals to connect them.
Charlotte Quong: a.k.a. Lottie, 6th year Slytherin, Prefect, values a good attitude above all else and has actually used her position to bribe people to fake cheerfulness. They definitely know one another, since they've shared classes for years. Lottie doesn't do enemies and she's not Nora-level abhorrent but they still probably don't get along swimmingly.