Hello, Thanavuddho, and welcome (in advance) to Australia
Sydney is a big city, even by world standards, with a very diverse population (probably 100 nationalities). Climate is cooler than Thailand but not cold - no snow, ever.
I think you will settle in quite quickly.
There are quite a lot of Aussies on DW for some reason but I can't think of any in Sydney. If there are any, they will probably introduce themselves when they see the thread title.