I’d reckon go to WA as coming from the UK spring, the weather although warmer than you would be used to, would be starting to cool off.
Fly in to Perth and get to Kalgoorlie and try a little prospecting as soon as possible. You will need to work out what you need and time to organise your travelling, camping, prospecting gear and access permits. You don’t want to be too far from a large place like Kalgoorlie where you can do all that conveniently.
After the winter there and other places in the very extensive WA goldfields and with some experience under your belt, I‘d consider heading to Victoria in about late September. The Victorian goldfields are more compact in size but offer good rewards for experienced operators who can work the deeper ground.
Approaching Autumn, I’d then think about Queensland.
Just my thoughts, but most important get prospecting as soon as you can because that is the quickest way to work out what you really need if you want to be successful.
Edit I’d second Moneyboxes recommendation regarding phasetechnical who provides good support to all our members and who could probably do a major items package for you. Remember though there are lots of other little things that you will need from eskies, clothing, picks, chisels, hammers and other tools you will need on the road and out in the goldfields.