Hey I'm in Perth. Moved last December. Congratulations on an excellent decision, but good luck getting in, you know Western Australia borders are SHUT, even if you are Australian and living in Sydney or Melbourne, you cannot go to Perth now. We have zero Corona cases in the last 48 hours, reopening schools on April 29th, but not allowing anyone in or out. Even the mining industry is looking for locals to drive trucks and dig shit out of the ground now because all the fly in fly out workers from the other states of Australia not allowed to fly in to do their jobs.
For your MPF, you arrange all this in HK. For example, my MPF is with AIA, so I need to request with AIA Hong Kong to cash it out. If you don't do it before you leave HK, you should be able to do it later anytime you want as long as you keep a bank account in HK and they deposit the funds into your HK bank account. Or they might issue you a cheque and then you will need a friend or relative in HK to deposit into your HK account for you.
Don't bother trying to convert HK MPF into Australian superannuation. There is no pathway for this, also no point since all Australian super contributions are taxed at 15%. For Aussies, it makes sense to deposit extra ino their super since 15% is much better than the 35% tax they usually pay. But for converting from HK to Aus, tax has already been paid in HK so you will just be paying tax for no reason at all.
Also as @pin mentions, if you or your partner taxable income in HK is over $200k, you should sign up for the MPF TVC account now and get a free $10k 'departure gift' from the HK government before you leave. Actually you should have done it before March 31st, now might be a bit trickier if your income for 2020/21 year is only a few months. But anyway, this process involves opening a new TVC account, claiming the benefit in your final tax calculations, then cashing out both your regular MPF and TVC MPF at the same time.
To be honest, I haven't cashed out my MPF yet. I was suppose to be in HK in Feb and March and was going to do it then but my trips were cancelled. Now the value plummeted . Not in a particular rush to cash out right now but contemplating a few different investment options now, buying some more land in Perth etc. I'm just refinancing my Aussie mortgages first @ 2.09% interest rates fixed for 3 years which is just unbelieveable that interest rates in Aus are lower than HK now, they seem to have followed me from HK to Aus