@Mark.1 If you are certain that you will get an invitation soon (considering your points, ISCAH prediction and etc), you may prepare the NBI Clearance and have the Medical exam prior to receiving an invite. Ang advantage nito is once you get invited, ready na lahat ng requirements mo and you can immediately lodge your visa application. However, please note that your initial entry date (IED) is dependent on the expiration of your health assessment and NBI clearance which are both valid for 1 year. For me, mas okay lang na gawin ito if certain ka ng maiinvite na rin soon, panibagong expense din kasi if ma expire lang sya.
On the other hand, if you want to be sure muna and want more time to prepare before your initial entry in Australia, pwede din naman na gawin mo nalang sya after receiving an invitation. Hindi naman din sya magtatake ng too much time, unless siguro if may HIT yung name sa NBI or need mo ng additional procedures for your health assessment. Yung iba mas prefer nila ito para mas may time din sila to prepare for their big move after the grant.