As far as 1/2, a fair bit of it is just an extension of those units in 3/4 (Dispute resolution, adversary system & jury, criminal and civil, VCAT... actually like everything but the constitution), but 1/2 isn't necessary.
That teacher ATAR is talking about, well he is my teacher and I understand where he is coming from, but I know plenty of people who picked up 3/4 and got pretty good scores. In legal the difference between a 45 and 50 isn't much.
So what you should do is go over that book I linked you to with the chapter that Werdna talked about (Intro chapter, has a rundown of important info) and then make notes based off the study design. Don't neglect legal throughout the year but its not something you should need to memorise, really just understand.
Also, here are my
Unit One and
Unit Two notes. They were pretty quickly done but I got A+s for both exams, if that counts for anything. Not the greatest but should be enough when coupled with Justice and Outcomes.