NEVER listen to anything an embassy tells you about getting an extension in Thailand. Extensions are done by immigration which is a completely separate government agency that has nothing to do with the MFA and they don't know each other's rules.
If you want 5 months in Thailand, you can apply for a 90-day non-O visa based on marriage from the embassy before you leave. Once you're in Thailand, you can then apply for a 60-day "visiting Thai family" extension based on your wife, which should get you around the 5 months you are looking for.
You'll need to make sure your marriage is registered in Thailand if you want to apply for that extension, or make sure you get your marriage certificate legalized properly by the Thai embassy before traveling to Thailand if it's not already registered.
If you do it this way, you won't have to show proof of funds in Thailand. The way the embassy mentioned would require you to have 800,000 baht in your Thai bank account as you cannot use proof of income because the US embassy does not do income verification.
Yes you can get almost 2 years, but you'll need another year of insurance. And then your only option will be to go back home to apply for a new non-OA visa or to apply for an in-country extension using money in Thai bank.
Correct. But note that if you want to apply for an extension in Thailand, you will need money in a Thai bank or proof of income from your embassy/bank transfers. Also you can only get the OA visa from the embassy in your home country, and it has a mandatory insurance requirement.
you would be able to get a letter/email from the BOI and they have a YouTube video interview with the head of the agency specifically saying that people working in Thailand on LTR remote worker are tax exempt