Gavin,
I've been living in Melbourne off and on for the past few years, so hopefully I can say a few things somewhat useful!
Melbourne's a pretty nice city - and supposed to be one of the best cities in the world to live in. (I'm not a huge fan myself, but I haven't really had time to integrate myself into any community here.)
I would definately recommend a trip down the Great Ocean Road just outside of Melbourne. Apparently you can do it in a day, but a weekend trip is a perfect amount of time! (You can my description of the trip on my blog here - http://blog.svandermark.com/index.php/2 … ocean_road.)
There are a lot of good restaurants in town - something Melbourne is known for. I've been to a few, but on a student's budget, I don't eat out a lot! But it's a very multicultural city - so you should be able to find all types of food. You'll certainly find Japanese food here - but I can't really comment on the quality, because I've actually never been. (Which I'm surprised to realise as I write this, although I'm not sure I'd be the best judge anyways. I'm certainly no expert.)
As far as there being an Asian community - there certainly is. But I'm not too sure about the Japanese community. I'd be surprised if there wasn't though.
Some places to visit in the city are St. Kilda - a nice community by the beach, and the Dandenongs - 'mountains' (really just hills) that are in a temperate rainforest. I can't think of anything else off the top of my head. As a student, though, I can't afford to do a lot anyways!
It sounds like you'd be coming over the winter. Bring warm clothes. Being a Canadian, I'm used to the cold, but I can't stand it here. while it doesn't get too cold outside, the lack of indoor insulation and heating is shocking here! In general, I'm so much colder living here than in Canada. I can't stand the idea of wearing outdoor clothing (jackets, etc.) indoors - but that's normal here! I find it can also get quite windy at times, which drives me nuts! But overall, it's not too bad.
Despite all this, there are some things I really love. I live in a suburb a ways from downtown. There are a lot of native trees and animals. I love the smell of the eucalyptus trees, especially after the rain. And seeing the rainbow lorikeets, which are around a lot, is also really great! And of course, the kangaroos! And I generally find the people very friendly - even compared to Canadians!
Other things that you could do here (but I haven't gotten around to yet) include a trip out to one of the many wineries around the city (they have great, cheap wine here!) or taking a trip to Tasmania, which could probably even be done in a long weekend - it's so close! Adelaide is supposed to be a nice little city that you could also visit in a weekend.
All in all, it's a nice place to live. But if you can also take a bit of time to see other parts of Australia, I'd highly recommend it (even though I've yet to have the chance to see much!). For example, the Uluru (Ayer's Rock) and the Great Barrier Reef would be great trips to take - you'd probably need about a week for each.
If you have any other questions, feel free to ask. I'll do my best to answer! Hope you have a good trip if you do go!