It should be easier to hit on "bad" homework, because there are more things that you can give advice on, where you perhaps could give tips on how to make a better and more improved piece of homework.

message staff

Even though I am not Australian, then I think it is a wonderful idea. We have three English speaking sites (where two of them are in the almost same timezone), so I think it would be amazing for the people, who are from the eastern parts of the world. That way they can be able to play Quidditch at a time, which isn't when they are at work or when they are supposed to sleep.

I hope this becomes a reality for all the Australian people, who are wanting a nice community, which is in a timezone that allows them to be wonderful. 

There are already dormitories :)

It is not 180 words, it is 180 characters, which should be easy enough to hit.
This is way better than feedback, which is just: "Hey, this is good. Good job." Which is already 23 words, so I don't see why you can't write things such as constructive criticism to the homework.
Perhaps the person hasn't written hasn't written a very long assignment, but then try to give ideas for how they could do it better in the future.... also look at that... I have written far more than 180 characters just writing this reply.

No, you cannot. You can apply to be a member, but not apply to be a leader.

This is something that you have to ask your plot leader about, as this is a thing for individual sites.
Feedback is more a thing for every site.

In what way does this go more in depth?
Topics are used for interaction between people and not just yourself, and you are not really allowed to use a lot of NPC in topics anyway, but you can do that in the backstory.

This can be done i either hallways or classrooms

Exactly! The Past forum is to interact with other people, if you perhaps wanted to have a chance to look at their childhood with another person :D
I have a few relations with people, which would benefit greatly from having topics in the Past :D