Yeah following up to this I totally agree. I would recommend instead doing a spreadsheet and recording every question you get wrong for trial/hsc preparation - sort of like a mistakes handbook in a sense, just digitalised and neat. Start on trials and past papers early (tHSC.com), you won't have enough time to do the more niche schools if you start later, save the actual hsc papers last, usually the are actually easier than the top nsw schools trials. The order you would typically go is Cambridge textbook exercises to build a foundation, then enrichment if you are competent enough, and I would go straight into real exam questions. Unlike english, in order to get better at maths is to just surround yourself with various types of questions with ranging difficulties. If you can get all the generic questions down and dusted, you can answer the majority of mc+q11-12 (that is already like 60% of the paper, note a 65% in 3U raw is already equivalent to a band 6). Question 13-14 is where you start applying a more extensive knowledge of the syllabus, but then again, with the correct preparation, it should be a breeze. Since 3U incorporates a lot of different topics, I would recommend to know a decent amount of each topic, filling up any misconceptions and weaker parts.
edit: also if familiarise yourself enough with different topics, you wouldn't even need the formula sheet since they should come naturally to u. (of course with the exception of sums to products/products to sums - those don't even bother).