In my opinion, I think it is best to have all your paperwork done before you apply. That way, you know it is all done and you won't have to think about it again until the CO asks for your background check and medical.
The NOIM can be completed with only one person. The marriage celebrant will ask to see your fiance's paperwork once they arrive in Australia. The date and place you put on the NOIM doesn't matter at all, because CO's know that is takes time for PMVs to be approved. If a marriage celebrant says otherwise, then find someone else who actually knows what they are talking about.
I am the sponsor of an amazing American!
Visa: PMV (Subclass 300)
Submitted: 4th Nov 2015
Medical & FBI Check Request: 18th Feb 2016
Visa granted: 2nd Mar 2016 (119 Days)
Visa: Partner Visa (Subclass 820)
Submitted: 18th Nov 2016
National Police Check for Sponsor Request: 30th Nov 2016
Visa Granted: 3rd Jan 2017 (46 Days)
Visa: Partner Visa (Subclass 801)
Application Submitted: 4th Nov 2018
Police Check for Applicant Request: 26th Sept 2019
Visa Granted: 16th Oct 2019 (346 days)