Don't do ALL the textbook questions! Just do the ones set by your teacher to understand the basics and to build up on speed/accuracy when tackling easier questions - but invest most of your time and effort in harder extended response and application questions.
My school used Maths Quest which doesn't have as good of a reputation as Cambridge, but regardless of textbook, you should always be aiming to go beyond.
When preparing for SACs, my approach was
skim through textbook exercises --> textbook revision questions --> extension questions and extra worksheets --> past SAC's
As for the final exam, my approach was
Mistakes logbook --> extension worksheets --> company exams --> past VCAA exams.
I didn't use other textbooks, nor did I purchase any commercial resources such as checkpoints, course notes, or topic tests. I highly recommend approaching your further teacher and the head of VCE maths at your school as they will likely have TONS of free resources to give you. GL!! xx