It's not *that* difficult to get in. If your year 11 reports are good, and if you've gotten above 35 for any year 12 subjects you did this year, then you're pretty much set.
As for time consuming, I found the travel to be the most difficult part. So, if you take public transport, I'd advise you to do at least some work in transit (I did Lit so I spent about 90% of train time reading). You will probably be required to do more independent research (which isn't bad - actually kind of fun) than in the VCE; you'll also have to be more responsible for making sure you know where you're supposed to be and when things are due. Also, you have to make sure you know what resources you have. You're responsible for figuring out how to use the library, SuperSearch and online class resources (e.g. accessing lectures online). It's not really difficult. If you put in the same amount of effort as you do for your VCE subjects you should go very well.
I learned on-campus, though. I believe the school centre experience would be a bit different though?