I do plan to keep my retirement visa if I leave, because if I want to move back, they may raise the amount you have to have on deposit to an amount I can’t afford. 
if you can get a tax ID and give the number to them, they will stop deducting the tax. I think the tax is 15%, and it’s possible to file a tax return each year and get the money back, but the process is very cumbersome.
Thai people often depend on street food, you go buy what you want, put it out on the table, family style, and dinner is served. The only cooking implement you need is a microwave. They often have a kettle and a rice cooker, but we buy food and rice already prepared on the street, is cheaper than cooking. I have a big old apartment with an old-fashioned, two tub wash machine, and there’s a set up to hang the laundry out the window under an awning. When I lived in a small room, I washed all my clothes by hand. The building has coin machines downstairs, but I never use them.
it depends on your citizenship. The US, British, and some other western embassies no longer issue the resident certificates. That lose you with the immigration department. And some provinces, as others have mentioned here, you can go and fill out the form and pay them and they’ll give you the certificate on the spot. Bangkok however, requires you to have done at least 1 90 day report, and then you have to have theresidency certificate posted to you, they don’t give it to you over-the-counter.
you will have to apply for a tourist visa, B1 B2. They will consider the country of your passport and its visa requirements for the United States. They will be interested in your ties to your home country, so that you’re unlikely to stay illegally in the United States. If you want to bring your Thai spouse, they will have to do the same, and it is hard for many Thais to get the visa, unless they have something like a long-term corporate or government job, house in car, children, etc. in Thailand. As in many places, the US Embassy in Bangkok is not friendly to giving visas to non-western people.
they will rarely give tourist fees to people who admit having an American partner, because then, once arriving, you can get married and seek adjustment of status and get a green card. They want the girlfriend to get consular processing that takes about two years.