I've been an expat for over 20 years. For the moving side of this - you've had a lot of good advice above. Take VERY little apart from the essentials (basically the work clothes you need to start off with that fit you) and minimize on everything else.
Here's a tip - for small things you want to take, that don't weigh much but will fill too much space in your luggage - post them ahead to an address or friend that you know
For the initial flights over - max out your luggage at the time of booking. Add the maximum possible weight to give yourself some wiggle room, but STAY BELOW IT.
Well ahead of leaving Oz - lay out everything you think you will take, and then pull out everything you can buy there on arrival.
@Flashback has also given some sound advice. Since your OP we have no idea of the location or details of your upcoming move. If you have to move around after arrival, it will be helpful to have bugger all to move with. This is very good advice
OP - you also asked what should you leave? Leave everything you can, if you have family or friends that will be happy to look after a few plastic tubs in their garage or storeroom.
Spend time WELL ahead of travel getting your external hard drives up in to the cloud so you don't have to take them. Especially if you have any big externals which aren't portable sized
Finally - where are you going to (where is the job) and where do you intend to live? You said UK but no further info. Also when? Lead time is everything