The distinction between the temporary and permanent visas is confusing. One automatically leads to the other. You apply for both together, and the ridiculously high cost (one of the most expensive visas in the world) is inclusive of both. You cannot apply for only one portion.
Think of the temporary visa as a probation period. There is no rhyme or reason to it (that I know of) but sometimes the temporary and permanent visas are granted on the same day, sometimes years apart.
If you are issued with a temporary visa, it is valid until your permanent visa is finalized. In other words, valid until the permanent visa is issued or declined.
If you are issued with a permanent visa, it is valid for 5 years. You are then on the pathway to apply for citizenship or other permanent resident visas.
My main concern if that the visa doesn’t expire if we don’t go there within 5 years. I don’t want to loose 8,000 aud. I will look at the resident return visa.
Just to confirm/clarify - you must move to Australia on or before the date on your Visa Grant Letter. This is usually 12 months after the Visa Grant Letter is issued.
If you don’t move before the date on your Visa Grant Letter, the visa will be cancelled and effectively expire. Bye bye $8k+.
If you do move before the date of expiry, then you have the time it takes to grant a permanent partner visa (ie the time you spend on a temporary visa) plus 5 years (the length of the permanent partner visa). You must be resident in Australia to apply for a Resident Return Visa.
The link in my earlier post can give you more information about visa pathways and how to apply. Click on all the tabs. You could also consult a migration agent in the UK or check out Aussie expat boards.
A lot of people have walked this path before you and can give advice but the most trustworthy will be the information provided by the government in the link above.