Scott,
When they hatch lacies are around 20cm/25cm long (give or take a few cm - I'm really not good with estimating lengths, but you get the idea).
As with any lizard, if you feed them every now and then they will only grow at an average rate. If you feed them alot and pump some heat into them, they will grow a lot quicker. Problem with overfeeding them though is that they tend to become obese a lot in captivity because they don't seem to exercise as much as they have to in the wild.
I'd say your tank will last a good year but after that I'd move it to a bigger enclosure, or maybe even outside. I'm not saying it couldn't still live in that tank, I just prefer to give my animals heaps of room.
As far as your aviary goes, plenty of people keep them this way successfully. The problem I have with aviaries is the roughness of the mesh. I had my Sand Monitor in a dog run for 2 days and he absolutely wore his nose down and bled unbelieveable. It was incredibly frightening and depressing that he would just rub and rub. That's why I give my animals heaps of spcae too - they don't seem to want to get out as much and so they don't rub.
Remember that I don't keep Lacies at this stage (but have met and talked with over 15 people who do) so my advice is just from what I know of all these other people's collections. I do intend to get a few lacies at the end of the year (budget permitting).
As far as anything else goes, I wouldn't give him a really hot enclosure - just similar to your Sydney weather. You don't want him to become too accustomed to a bit of extra heat and then whack him outside in the cold when he grows up
Simon Archibald