I am studying first year Biology at Monash at the moment, which entails both BIO1011 and BIO1022, which I am pretty sure MEUP kids do alongside with me (I've seen a few high-school students in my lecture).
In my opinion, having not done VCE Biology, VCE Biology itself will give you a huge advantage in Semester 1. I am pretty sure most VCE Biology kids did not learn anything new until the 8th week of Semester 1, and even in Semester 2, they still have learned some of the concepts in VCE. If you do VCE Biology you'll alleviate a lot of potential stress, for example in VCE you cover Mitosis and Meiosis quite slowly from what I hear. In Uni Bio it is thrown at you all in the course of two lectures, thankfully I had friends who helped me understand it.
As for the workload, if you didn't do VCE Biology, like me, I'd say you'd expect to dedicate 8-9 hours per week of private study, if you want to do well (don't cram, I am doing that now due to huge amounts of work and it is a horrible feeling). If you do VCE Biology I'd honestly imagine you'd be doing 2-3 hours per week until you get to week 8 where you learn about Plant diversity.
In terms of getting high marks, it's pretty difficult (subjective comment) to do well in Biology at a tertiary level, you really have to know what you're talking about and in your prac reports it'll show if you won't. This forms a large chunk of the assessment and it's worth doing well in. The exam is all multiple-choice and it's relatively straight forward if you attended/watched lectures and grasped the content. 5% of your assessment comes from pre-lecture readings and as long as you read the prescribed pages then you should be able to get 4.5% of the 5%!
I hope that helped and feel free to ask any more questions if you'd like!