What is be best way to travel the east coast in January/February for 1,5 months? Cairns - Sydney, or Sydney - Cairns?
Travelling with Greyhound and staying in hostels mostly making my own food is AUD 4000 realistic?
I want to spend a few days at the places i stop at, and I want to do a Whitsyundays and a Fraser Island tour..
If not realistic, how much is realistic?
AUD 4000 for a month and a half is plenty. A lot of that will be sucked up by doing activities/tours (keep an eye on that), but it gives you a budget of nearly $90/day, which should be plenty for those activities/tours, the bus, staying at nice hostels and cooking yourself sumptuous dinners.
However, are you aware than January/February is the middle of the wet season up north? I remember the humidity being horribly unpleasant in Brisbane in January already. Further north than that you'll be getting frequent torrential rains.
I'd personally spend those 1.5 months doing Adelaide to Sydney, and then not going north to Brisbane and further before March. (If at all possible with your itinerary; don't know when you're set to leave Australia again.)
I leave for SEA in the middle of february so I have to do the east coast in January/February, but seeing as I am from Nothern Norway bad weather is what I am used to And I love the smell of rain in Australia