IMO, it would be the most important to determin the role of carriers for Australia.
The most probable role is intervention in small Pacific countries northeast from Australia ( like Papua New Guinea, Solomon Islands, Fiji, East Timor ) in case of coup ( imposing democracy ), civil war ( imposing peace ) or evacuation of Australian citizens.
For such duties, you don't need a large CTOL carrier. Even a small air group of 6 Harriers, 10 Sea King ( transport version ) and 2 Sea King ( SAR version ) will be enough for that. OFC, airgroup can be tailored, so that attack helicopters from Army can be taken instead of Harriers etc.
Second role is taking part in coalition efforts. Like say intervention against Iraq. There such carrier, with airgroup of dozen Harriers and few Sea King ( SAR ) and few Sea King ( ASW ) can do the trick, that is- show that Australia is there, not play main role in war.
Third role is, securing sealanes. In modern day's that's something like fighting against piracy in Horn of Africa. There you don't need Harriers at all. A few Sea Kings ( transport ) and few Sea Kings ( SAR ) is enough.
Another similar role is- ASW. There you also can play a good role with 10 ASW Sea Kings, 4-6 Harriers ( for air protection, if nescesarry ) and few Sea Kings ( SAR and AEW ).
Fourth role is- combat intervention. The only situation that is imaginable to me is preventing Indonesian invasion of E. Timor. There small carrier can play some role, but can't be decisive weapon. Nontheless, if oponent isn't too advanced ( and Indonesia isn't ) it can be very useful.
Attacks on Cam Ranh and so, are IMO, clearly out of level ( and also out of interest ) of Australia ( to do it alone, without USA, so clearly US carriers should be nescesarry for that, but Australia can give a hand there, as said in role No. 2 )
So, IMO, two small carriers like Garibaldi, Invincible or Principe de Asturias are just enough for needs of Australia.
If we assume that they have operational availability of say, 65%, that's one carrier allwasy ready, and another ready 30% of time. If both are ready, one can be on sea, and another in port, ready to take LPH role, or in training etc. If only one is ready, his airgroup can be tailored that he can serve as aircraft carrier, LPH or big logistical vessel.