The email you get will be your visa.
You will show it to immigration when you enter the country and they will do a arrival stamp with your 60 day stay on it
You wifes address in Thailand will be accepted.
Ignore the work permit part. That is only for those working here for their family members to get a non-o visa.
The equivalent of 20k baht in a bank in Australia will be accepted.
It uses the info from the previous report to complete it.
Your extension of stay expiring (it is not a visa) next month has no effect on doing a online report.
Did you change any info when you did the 2nd report?
The best way to avoid problems after doing the first report is to enter your passport number and nationality and then click the hourglass to complete your report.
You would only need to show proof that you had been working here and that is where the 800k baht came from.
Also when apply for the non-o visa if you have had the 800k baht in the bank for a long time the will waive the proof it came from abroad requirement.
You cannot change non immigrant visa types while in the country.
You can only change the reason for your extension from retirement to marriage. No insurance would be required it you did the change,
A WP3 is only used when a person is outside the country.
A standard work permit application form is used while in the country and a work permit application approval letter is then done.
I see not reason for you not being able to use your new passport number to do your online report. But it may depend upon the officer processing your report.
It depends upon where you read the info. Some say required and others state it should cover your length of stay.
The FAQ's on this site does not mention how long the insurance must be valid for.
https://consular.mfa.go.th/th/content/thailand-pass-faqs-2
Yes you must have 400k baht in a Thai bank on the day you apply for the non-o visa.
You can also apply for the non-o visa up to the last 15 days of the 30 day extension of your visa exempt entry.
If you need more time you could also apply for a 60 day extension to visit you wife.
If your change of address entered in their system you should be able to do your 90 day report online but it could depend upon the officer processing it.
From the 18th of this month onward 90 day reporting will be done at Chaeng Wattana. They are closing the MTT office.
If a work permit office would accept a work permit application and issue a approval letter for it you could apply for a extension of stay based upon working for a company.