The only real criteria you need to meet for a PMV 300 is
You are both of age, and are free to marry each other
You do get married within 9 months of the Visa Grant
You complete/supply all the criteria requested in the application (see below)
The IMMI wording is;
You must enter Australia on the Prospective Marriage visa before the date specified on your grant letter.
You must have married your prospective spouse before your Prospective Marriage visa expires.
You can get married in Australia or any other country. Your marriage must be valid under Australian law.
Amongst other items, the application does require you to provide an Affidavit from a person known to you both, that can declare that the relationship is genuine, and your making plans for marriage etc
All the facts and steps are here: https://immi.homeaffairs.gov.au/visas/getting-a-visa/visa-listing/prospective-marriage-300#HowTo