Hi,
I am planning a trip to SE Asia (Vietnam, Cambodia & Laos) and Australia (Melbourne, Sydney & Cairns) for approx 4/6 weeks, depending on my work's holiday approval. Does this seem like a reasonable timeframe? Also, would appreciate any advice on the route or must sees.
Thanks for any help in advance 
Hi.
Where are you starting from?
Research the weather for the time you be on your holiday for each country.
Some months in Southeast Asia you go through a rainy season. (Rainy season is not all bad because this will be low season for flights and hotel pricing. Often rain does not last all day long. But, if you have a GREAT interest in beaches - look into what is available for your time frame.)
Unless you have some sort of deal with your airline - so far it looks like a bunch of one way flights! For me, some of my round trip tickets to Southeast Asia were close in price to one way flights. (Do the math.)
One suggestion is to do round trip to a major city in this part of Asia and use cheap connecting flights to get to nearby countries or even other cheap travel. Return to first city for the flight back home.
Or do AU and NZ for one holiday period. Southeast Asia for another time.
Pull up your favorite airline and price out the cost of flying for the month you are available. Looks like a big chunk of your time could be in transit. But some people like this.
Kind of like that old movie - If It's Tuesday, This Must Be Belgium! (Except for being in a different part of the world!) 
Come on back.
Forgot this:
Also, would appreciate any advice on the route or must sees.
-
This is sort of up to you. Some people a "must see" could be nightlife. 
Someone else their "must see" could be beaches or or old temples, historic places, etc.
Quick, and free, Google type search can give you info to think about. Old Lonely Planet books can help with stuff to see and do, (But hotel suggestions could be off in current pricing)
This TP Forum has info for various parts of the world. Find "hamburger" button, top left where it says MENU. Locate the part of the world you have an interest in for details.
https://www.travellerspoint.com/guide/
Up to you!
[ Edit: Edited on 24 Jan 2025, 02:21 GMT by karazyal ]