Can I extend my stay in Thailand on a marriage visa with a 30-day visa exempt entry?

You are mistaken. Unless you come from a country whose consulate here issues an affidavit of income from abroad notary letter stating you get at least 40K baht a month in income from abroad you need to have the 400K baht in your account BEFORE you apply for the 90 day Non-O visa inside the country at the immigration office. and for the year extension that 400K baht needs to be in your account for 2 months before you apply.

here's a thought, get a single entry tourist visa, come in get stamped in for 60 days, extend that the ONE time you can for 30 days then apply for a 60 day visit thai family extension based on marriage. That gives you FIVE months in country with NO proof of funds.

so difficult to do!

E visas were introduced september 26th no need to submit your passport

Yes

You can do what you describe but you'll need 400k in the bank to get the 90 day non O.