Hi, A UK drivers license is valid for 12 months after your arrival date. We renewed ours really easily at the local rego ofice, just be prepared to queue, not very expensive and they came in the post within a month.
Rego in SA provides 3rd party insurance as part of the cost, not sure if that's the same is WA though.
Register for Medicare as soon as you arrive and if you're coming to SA don't forget to take out Ambulance cover. Should you be unlucky enough to need an ambulance, if you don't have cover then you get stung with an $800 bill!
Good luck, enjoy