Is it easier to become a dependent after marrying a work permit holder in Thailand, and should I get a visa before arriving?

Make sure with your spouse's employer they are going to support your visa/extension.

At the risk of stating the obvious, print the e-visa paperwork and don’t lose it - immigration wanted to see it for my non-O application as well as for the extension application, despite the corresponding stamp in my passport. There was a moment of stress when I showed them the email with the circled check mark, which was inadequate - they needed to see the page that has the embassy seal in the header, and I had stapled it under the check mark page, so we skipped by it several times.

The visa you get AFTER you're married to another foreigner who legally works here is a Non-O visa based on what's called "trailing spouse" and you can't get that BEFORE you wing your way here because you're not married yet 😮

The best thing you can do is get a single entry tourist visa from the thai consulate in the US before you come here (it's all online via the eVisa website). That will get you stamped in for 60 days when you arrive and you can extend that for 30 more days at the immigration office for 1900baht.

Those 90 days should give you enough time to get the documents together to get married, get them translated, get the marriage registered at the local Amphur and still have enough time left on your stamp to apply for an in country Non-O visa at the immigration office based on being married to a foreigner who legally works here. I doubt you'll be able to pull it off with just a visa exempt. Spend the 40 USD and get the single entry tourist visa