Do I need to get my marriage documents endorsed by the Ministry of Foreign Affairs in Bangkok for a Non Imm O visa based on marriage?

You can do it in Hua Hin at bluport. No qeue. Get it back in about 3-4 days.

For what it's worth this was how I did it for marriage registered in NZ. 1. NZ marriage certificate legalized by MFA in NZ before coming to Thailand. 2. Visit NZ Embassy in Bangkok to certify. 3. Down the road to Express Translation Service who arranged translation, processed with Consular Services and sent to me at home address (I was happy to pay them to save me running around doing it myself). Around two weeks to receive everything. I believe they can assist with getting your Kor Ror 22. Our immigration office didn't require Kor Ror 22 even though it was on the handout of required documents, the translated and legalized marriage documents were adequate but that's office specific I guess.

yes need mfa approval prior to going to amphur

You may also need to do the same with a copy of your passport. In my case, it was also required that I do the following. (I see you are from Sheffield, and I'm from the US, so I don't know if there are any differences in the process for your embassy in step #2 below)

1: Get a photocopy of my passport (just the biodata page, and we did the signature page above that too; it's all one photocopy when a US passport is opened to the biodata page)

2: Go to the US Embassy and have it notarized as a certified true copy

3: Get that translated into Thai (a "certified" translation, as we did with our marriage documents)

4: Get that approved/certified/stamped at the Department of Consular Affairs.

It was required for us to register our marriage and get a Kor Ror 22. I've heard of some say it wasn't needed, and others say it was needed. So it may be different in different amphurs. It was definitely needed in our case. Not optional.

So if you are going to the Department of Consular Affairs anyway for your marriage docs, you may want to get the passport copy done at the same time.

Sounds strange since it was already endorsed by the Thai Embassy which falls under the MFA.

Your not going to have time that’s why people do there extension a month in advance you’ll have to start over when you return

Yes you have to go to the MFA

Yes it is needed.

It is necessary