I learned to fly in Australia when I was working there, but that was a while ago (2000/2001) - so things have probably changed a bit. With that said:
I'm not sure how much the requirements for airside security passes have changed, but you only needed an ASIC (the fully blown pass) for major airports. They were being introduced in 2002 just after I did my PPL in Australia, I got one initially and never bothered to renew it.
Australian class 2 medical is very similar to the EASA one - I renew both of mine at the same time in the same appointment in the UK; I'm sure this is do-able in major cities in Australia too.
One useful thing I discovered when using my Australian PPL as a base to get an EASA PPL is that there is some reciprocal agreement re: RT licenses - so that is something that may be useful for you (no requirement to do any additional RT tests).
Most of the AU air law is very similar to the UK's.
Australian license requires a BFR every two years - so no revalidation by experience, but the BFR flight test is similar to the "one hour instructional flight" so it is pretty similar.
There's far more emphasis on things like submitting flight plans even for short-ish VFR flights (mandatory if you're going into a remote area which can be surprisingly close to the main cities), and my personal experience is that in Australia, people learn to fly because its a damned big place and they want to get from A to B. Coming back to the UK, it felt like people fly to mimble around on a Saturday afternoon - generalisation, I know, but I think there's truth in it.
Paul.