Generally, they have not been requiring anything in the way of proof. There have been a few scattered incidents of people not getting approved but generally you should just be able to apply for the covid extension without any supporting documentation.
Not sure about the getting married twice thing. Don't you need proof from your embassy that you aren't already married to get married in Thailand? Seems like getting the exiting marriage recognized in Thailand is the better way to go.
You should use her Thai passport information to buy her ticket. She will leave the US on her US passport. Enter Thailand on her Thai passport. She should travel to Thailand using her Thai passport.
Agree with Dan on Q7. As far as Q8 if there has to be something there you could put a copy of your passport photo ID page. Maybe it's not polite to invite yourself to a party, but at least it gets you past the question.
Seriously, I don't think Q8 really gets examined much, it probably should be a skippable field.
If you run out of time to obtain a visa you can arrive in Thailand with a visa-exempt entry which will get you 30 day permission to stay which can be extended another 30 days. From the visa-exempt entry you can apply for other extensions of stay. It's no worse than the Tourist Visa (except the tourist visa gets you 60 days permission to stay instead of only 30 for visa-exempt).
JD Skate Using Wise with Bangkok Bank and choosing "long term stay in Thailand" as the purpose of the transfer will result in an FTT (Foreign Telegraphic Transfer) in your passbook which immigration recognizes as designating a foreign transfer.