So I'm feeling out the idea for a story focused on Cho during her final year, and I'd dig some outside perspective on a couple of points.

1. What other students are in their final year during HBP? So far I've got Cho and Marietta Edgecomb (presumably), Katie Bell and her friend Leanne (against, presumably), Cormac McLaggen, and Roger Davies (who could be a year older and finished with Hogwarts, but I want a wider cast to draw from). Anybody I'm missing that we know is in this year? Any other students that could conceivably be in the year above Harry?

2. If a student was just to take off from Hogwarts - just get on their broom and go, say - how easy would it be for them to do so? Harry has a good track record of disappearing off the grounds, but those tend to be in exceptional circumstances, and judging from both GoF and OotP there's nothing like a warning system in place that says if any student has left the grounds. How long would it take before someone raised the alarm, so to speak? Again, Harry is all the time sneaking about the castle in the middle of the night - could a student realistically manage to slip away some time after the evening meal and be gone all night, and not have anyone really notice they were missing?

3. Does Katie Bell play in the last Quidditch match of the year, or is she still too injured?

4. Are students allowed in other Houses' common rooms? Like, at all? The Gryffindor and Slytherin common rooms are password-protected, but you could argue that it's a hold-over from the Founders wanting to protect their trade secrets, and we see in DH that technically anyone could get into the Ravenclaw common room, and it's never specifically forbidden, as far as I remember... In the spirit of inter-House unity, could a student of one House sort of vouch for a student of another for access into their common room?

5. What's the process for students electing to stay at Hogwarts or return home over the holidays? Do they just notify their Head of House? And is it only over Christmas, or is there another break where students can go home that I can't remember because Harry's usually at Hogwarts come break time?

Thanks for any illumination people can provide.