Hi!
I did texts: Luke last year and absolutely loved it! (even though I don't particularly adore religion) ;P The course itself was amazing but the exam.......I think we were trolled 0_0
You can most definitely start looking at background information NOW (your first SAC will usually be around "background" of the gospel) and read some of Daniel Boch's stuff (he's the only worthwhile analytical theologian in my opinion, the rest contradict themselves too much).
I don't know if you have your special passages yet, but if you do, read them. Also, for Luke, 4:18 - 19 is the key of what Luke is about sooooo...read that.
Also, you'll find Unit 3 to be extremely easy (I got A+ on all my SACs with minimal studying), but when it comes to Unit 4....I thought I was going to die...literally, so don't be surprised if you're doing triple what you did in unit 3, in unit 4 (in terms of workload).
Finally, for essays and stuff - VCAA. However, I will point out that special passages deliberately change every year, so there is no point in reading exegesis analytical pieces on passages which are not in your special passages as the exegesis passages are based on the chapters for special study. However, for the essay, they could ask you anything and I mean ANYTHING in the gospel...and THAT's worth 30 out of 90 marks (30 for short answer, 30 for exegesis and 30 for the essay).
Good luck! If you need anything, I'm happy to help