Best time to visit
It depends on what you want to do and where you want to go. For the south of Australia, including Sydney, Melbourne and Adelaide, October to April is best, as this is summer. The tropical regions in the north, such as the Great Barrier Reef and Darwin, are at their most pleasant between May and October during the dry season. In the desert and outback, it can get extremely hot from December to February, while it is more pleasant between May and September. Overall, Australian spring (September to November) and fall (March to May) are an ideal time to travel in many regions. City trips are possible all year round.
Driving
For EU citizens, the national driver's license is sufficient in most federal states as long as it is written in English. Otherwise, an international driving license is recommended. Most states allow driving with a foreign driver's license for up to three months.
The road network is well developed, but there are long, lonely stretches with little infrastructure, especially in the outback. Some roads are only passable with a four-wheel drive vehicle.
Traffic signs and rules may differ from those in Central Europe. The traffic regulations also vary from state to state. It is best to find out about the local traffic regulations yourself before your trip. In Australia, traffic drives on the left, which can be unfamiliar, especially at first.
The speed limits also vary from state to state. There are strict penalties for driving under the influence of alcohol - some states have a zero-tolerance policy. You should therefore only get behind the wheel sober.
Phone
If you use your home SIM card, you will have to expect high roaming charges. These vary from provider to provider. You should therefore get an Australian or international SIM card if the Wi-Fi in your accommodation, restaurants or public places is not enough for you. I can recommend Airalo for vacationers.