CASA approval granted!
I got a phone call from CASA this morning to let me know that approval for launch was going through, and to ask a few questions about the tracking of the balloon. Hopefully I'll receive written confirmation today, and we can then start to look at organizing launch. 
Likely we'll aim for a weekend launch to make sure everybody is available - unfortunately current predictions do not look good for this weekend, though we may be able to launch in early February - but this is too far away to be able to predict at the moment.
CASA approval ongoing
Unfortunately I heard back from CASA today that approval has not yet been finalized. This means we can't legally launch this weekend. At the earliest we may be able to launch Monday/Tuesday next week, as CASA will only process my application during business hours.
Who knew a simple approval would take over 2 months to process? 
Launch delayed
Picked up an E size cylinder of Helium today - many thanks to Gary from the Elizabeth branch of Air Liquide Australia for making it all happen. I've also made up a balloon filler with a regulator for the cylinder & some hosepipe + PVC tubing, which looks like it will do the job well.
I have been hoping to launch this Sunday, as the weather has been looking very favorable. However, I heard back from CASA today, who are not yet done with processing my application. Hopefully this will be done sometime next week, and we can then start to look at launching. 