Hey Pep, really liking your journal
For essays, if you have a SAC-filled week, you can even just do essay plans or spider diagrams of what you may discuss or write about for that essay question. Don't be too stressed in having set responses to some for your GC. You might want to have a few phrases up your sleeve that you can apply to a broad range of questions to kickstart the conversation (then add in the relevant info or what a teacher I once had called 'the meat' you need to provide for that specific question, e.g. leisurely activities in your spare time and most importantly your subjective viewpoints, which examiners want.
Some examiners might have a slight prejudice towards memorised parts or responses, so chucking in some
relevant Chinese interjections (you can even use them when there's a tough question, to give yourself some time to give a 'sound' answer or keep the flow of the conversation going) will make your oral exam more of a conversation than a job interview and make the whole conversation less awkward for you and the examiners, and make you sound more genuine and even less scripted believe it or not.
Having a few phrases that are interchangeable, can allow you more time to prepare for your detailed study (where you want solid sentence structures, encompassing, a bit more presentation-like and get to your points fast (like when people are giving a pitch to sell something) so that you can give examiners a chance to ask questions and take a breather in processing what you've talked about. You can better show your attention to detail and efforts you've made in studying your topic/person.
Oh, in case if you haven't been told already. If you do make a mistake, correct yourself in Chinese, you won't get marks deducted and if you're not 'making a bit deal about it' you may even pick up some marks (obviously don't do this just for marks, but think of it as something to keep the conversation going).
When describing something using idioms or even adjectives, the examiners may ask you to explain them so make sure you have a clear example/s to use in your explanation, synonym/s or description in mind so that you can explain it in a way that is succinct and easy to understand. Other than preparing for the advised topics that may be asked on the oral examination, you should also be preparing the way you present yourself visually. Such as your facial expressions and body posture (i.e. to show confidence and sincerity). If you have a considerably large mirror at home or at school (that you can see the reflection of you sitting on a chair), you may want to practice e.g. facial expressions (yes very important), hand movements, head tilts, shoulder movements, and the slouched position when talking about something sad and etc. Yes, this is not a VCE Drama solo, but psychology is equally important to your fluency in the language. So don't neglect simple manners and kind gestures too.
Also, you might want to have a look at how natives (make sure they're from the main cities in Mainland China and conversing in Standard Mandarin, yeah there's an unofficial bias unfortunately) interact with each other in day-to-day conversations and pay attention to what sort of subtleties are commonly present in people's expression and overall demeanor.