Hello! That sounds like an exciting trip to Australia. Here's some advice to help with planning your adventure.

Best Time to Visit:
The best time to visit these cities depends on your preference. Sydney and Melbourne enjoy a temperate climate with warm summers (December to February) and mild, somewhat chilly winters (June to August). Adelaide is known for its Mediterranean climate, with hot dry summers and cool wet winters. If you want to avoid heat, it's advisable to visit Sydney and Melbourne in Spring (September to November) or Autumn (March to May), and Adelaide in Autumn (March to May).

Route and Accessibility:
Sydney, Melbourne and Adelaide are well-connected with International Airports. Domestic flights are frequent between these cities. Another option is to take the train or drive; the coastline view is fantastic. Buses, trains and trams provide accessibility within the cities.

Accommodation and Booking:
There are plenty of accommodation options in Sydney, Melbourne, and Adelaide. It's advisable to book in advance through reputable travel websites. Depending on your budget, you can choose from luxury hotels, bed & breakfasts, or hostels.

Clothing and Essentials:
It's recommended to pack a mix of light and warm clothing for these cities. Don't forget your sun protection like a hat, sunglasses and SPF as the UV radiations are quite strong in Australia. Comfortable shoes are essential for city tours.

Health and Safety:
Australia is generally a safe destination. However, it's always better to have travel insurance. Stay hydrated, especially in the summer. Don't forget to carry any personal medication.

Local Etiquette and Respect:
Australians are generally casual and easy-going. Respect local customs and maintain cleanliness, especially in public places. Tipping is appreciated but not expected.