what is the problem with supplying what they ask for if you have them? If you don't supply what they ask for you don't get the visa. It doesn't matter at all what you've heard as rumors about what other people needed, or didn't need. This only involves you, and what you are asked to provide. You cause a lot of stress for yourself by questioning this. Just give them what they ask for, and don't try to fight it. It is that simple.
it sounds like you didn't file your taxes last year, or you would have no problem supplying it. Bank statements just prove you have the required equivalent of the bt500,000, not wage payments. It also asks for your employment contract to be signed. Is it?
You seem to ideally think immigration entry is cut and dried, always following some rule you think exists. Entry into Thailand, no matter what visa you hold, is at the discretion of immigration. When they decide a person is trying to stay in Thailand long term on tourist entries, they will refuse entry, and they are not stupid. They know all the tricks. They also profile and stereotype, and use the comment section of their computer system heavily. The best laid plans to try and stay in Thailand on the wrong visa, visa exempt, entries, are caught pretty quick.
If she has Lao ID then she can fall under the guest workers program in Thailand. If she doesn't then she would follow the same requirements to work as you would.
Legally you can not get a work permit on any retirement visa extension, including to do volunteer work, and it is required. There are a number that do, and a small percentage of them get caught doing it, usually from a police complaint, then they are deported in lots of cases, and barred from returning for no more than ten years, with marriage having little influence. Most don't get caught, so it's at your own risk if you're one that does get caught.
it all depends on where you have the bt400,000. Savanaket now requires the bt400,000, or equivalent, in your bank account somewhere. Not necessarily in Thailand, but in Thailand you need the bt400,000 in a Thai bank first. In either situation it is first a 90 day stamp, giving you enough time to get everything together to apply for your one year extension. It also depends on how many days you have left on your original entry stamp into the country. Usually somewhere between 15-21 days, but I'm not sure of the exact days as it can vary between immigration offices.
If you are married to a Thai citizen then as soon as you get here open a Thai bank account and transfer bt400,000 into it right away. Also go to immigration with your Thai wife, and get the list of documents needed for your one year extension. When you have all the documents, and your money has been in your account (in your name only, not a joint account), for at least two months then you can apply for your extension. Just remember, your required bank letters can not be any older than 7 days. Everytime you are dealing with immigration concerning this extension always take your wife with you, or they won't talk to you.