First - check over on the Downunder & Godzone GA part of PPrune, you'll find loads of local knowledge there.
That said:
- CASA CoVs are valid for three months only. As I said on another thread, do NOT apply too soon, as they are required by some regs to process the application when it comes in (IOW you cannot apply for a CoV now with a start date in, say December)
- ASIC: this is a bit of a minefield. Mine was processed by CASA - but then lost in the mail (within Oz). CASA had to issue a new one. The chaps over at the D&G forum will probably tell you to steer clear of CASA, I must have been lucky, as they were very helpful and quick.
On a more general note, you're a lucky bu**er! The area around BNE is perhaps the best in Oz to rent airplanes, loads of possibilities.