What are the steps and documentation required for applying for a 90-Day Visa and extending it to 12 months in Thailand?

Unfortunately it is up to the individual Immigration Officer to request whatever they feel is necessary.

On top of that you have bank staff hell bent on refusing to let foreigners open an account.

Bank teller asked for Kor Ror 22 even though I had the MFA marriage certificate translation, so after getting the KR22 they just copied my MFA cert and ignored the KR22 - took 5 attempts of getting stuffed around, and I had all the paperwork they used the first time I went in.

The bank was the main hurdle for me, immigration was a breeze.

Why do you need a marriage certificate to open a bank account anyway?

Once you arrive register at your local immigration office TM30, registration letter for bank

Apply for yellow book and ID, get SIM,

Will probably need MFA copies of your passport, marriage certificate, birth certificate, I also got police clearance (which the bank took?)

You have 1 month to get your money into a bank account for the visa extension

Good luck and I’d avoid Bangkok bank and KTB

So far, the information given is solid and correct. If you know where you plan to stay in Thailand, you could reframe your question asking, what the requirements are for that specific immigration office. One thing missing from the information so far, is the need to get a Thai cell phone number and have the provider, (I use Dtac, but there are others), register the number to your passport details. You will need this when opening your bank account. For a relatively small amount of money, a visa agent can help you with this should your require assistance. Enjoy your time in the Land of Smiles and welcome.

No, there isn't. And there's a very specific reason for that.

In Thailand, the way things work is all power is given to the local level. What this means is that the requirements are based on what your local office requires. There's no way to say what your requirements are because it will not be the same for everyone. This is even at the embassy level when applying for the 90-day non-O visa, as each embassy can set their own requirements.

Once you get to Thailand, you'll need to get a certificate of residence from your immigration office in order to open a bank account. You will need to find out what your local immigration office requires for this.

Then when you go to open a bank account, you might have to try a few different bank branches, even of the same brand of bank, as each bank manager can set their own requirements for foreigners to open a bank account (do you see the theme here?)

Then once you get your bank account, you deposit your required funds, and then you will need to meet the requirements of your local immigration office to apply for the 12 month extension. That means when you go to get your COR from immigration, also ask them for their handout of requirements for the 1-year extension. Then you'll know exactly what's needed FOR YOU.

Then once you are settled in you can look at getting a drivers license maybe. This will also require a new certificate of residence from immigration (each CoR is only for one specific reason), and what you need for the license will depend on what your local Department of Land Transport requires, as they each have their own requirements.