@claireb7rg congratulations on being accepted onto stage 1.
Re the Australian check, the SW and/or agency do have some discretion over whether you need to do this. My SW asked me to do five different countries, one that I'd only spent a month in about fifteen years prior to my application. Her colleague later admitted to me that my SW had perhaps been overcautious and that a stay less than six months probably wouldn't warrant getting the check done. A friend of mine who had also lived in several different countries, one for about five years was not asked to do any overseas police checks because they were all more than ten years ago.
So I would first make double sure that it is required of you, and if your SW is quite sure that she wants it then just crack on and do it. From my experience, saying that I thought something was unnecessary or a big hassle if anything made my SW more certain that I should do it. I expressed concern that the one I'd only been to for a month would be unlikely to issue anything since they had almost nothing to go on, and she said that was fine as long as I still went through the process of applying. So I did and it came back very quickly to say they had nothing on me, which is all she needed to see.
All countries do this slightly differently, and some require more of you than others. One of mine needed fingerprints and a couple required me to present myself at the relevant embassy. Costs also varied greatly. I have had a look at the Australian one that I've linked to upthread and I have to say this is definitely one of the more straightforward ones. The form is short and although they ask for your addresses for the last ten years they don't ask what you did in Australia or where you stayed.
If it turns out you do need this check I would start on it sooner rather than later as you don't want this to be holding you up from progressing later. That said in spite of the delays I had in trying to sort out all the bits and pieces for overseas police checks the one that came back last was the UK DBS.