Brightsky,
Bad news: UMEP maths is tough (or is this good news

Good news: it is easily manageable. You will need to work steadily throughout the year, but there is also a long break between your final VCE exam and the UMEP exam, which gives you the time you need to prepare for that increment of 5 you are destined to get.
More good news: You get a credit for Uni, equivalent to Accelerated Maths, which means you can start doing interesting maths almost straight away at Uni. UMEP maths is a complete course in Linear Algebra, 1st Year Vector Calculus, with a few other interesting bits such as Mathematical proof and Induction, Complex Numbers, Solid geometry etc
All you have to do is do every problem in every problem sheet, plus the past 4-5 years exams, and you will get a very comfortable 5.
I recommend you get your hands on the two recommended textbooks, Thomas Calculus ans Anton/Rorres for background reading.
You will be issued with a UoM student number (which you will retain when you get there the following year), a library card, and access to the student portal which in turn gives you access to many online library resources which can be of value to you for subjects such as VCE English (eg scholarly book reviews etc)
Added bonus. You get to see your UMEP result via your student portal a few days before the VCE results come out
