If you have a C of V, you don;t need an ASIC or AVID, as these are only required for CASA licences. (Silly, isn't it)
However here in the West, if you want to go anywhere interesting you will need to refuel at security controlled aerodromes, so will need an ASIC.
You can apply in advance and this can save some time, but checks have to be made with immigration after your arrival. To make sure you have really srrived.
One of the hardest bits is getting people overseas who can verify your identity, this can be done by an embassy official (and I hear they charge like wounded bulls per document verified) or a doctor approved for CASA medicals, or your own doctor if THEIR id has been verified by someone on the list....it's nuts. Someone on the list of approved people, eg nurse, vet, phsiotherapist etc has to be qualifed to practise in Australia. Also an overseas person can usually only satisfy the requirements for the secondary ID if they apply for an state issued Aussie drivers licence when they get here. (easy).
Another hold up is getting the authority in your country to verify your licence details, you need to authorise them to give this info to CASA.
All of this used to be done in the field offices, but since being relocated to Canberra it takes weeks instead of hours even if all the paperwork is in order.
It's all completely ridiculous, and has almost completely destroyed the self fly holiday market, which was pouring billions of tourism dollars into the country until all this nonsense came in- Goana tours shut up shop because of it.
HOWEVER we are still getting people through these hoops, but you need to allow about 4-6 weeks. PM me if you need help.