but you won't get a year out of it. It's good for 6 months from the date it is issued so get it close to when you plan to leave and make your last bounce close to when it expires then you are done. Probably closer to 8 months in reality. But I'd say 33k baht a month will be difficult to live on in Thailand, particularly as a tourist if you're staying in hotels and travelling
only the immigration officer can tell you that. I know at my office they check this very carefully, that's why they insist on a full 12 months of bank statements (I usually get 13 months as if I'm even one day short they won't accept them)
Seems to me there are a number of issues here and they will all need addressed in one way or another. I'm guessing you used an agent due to not having the 800k baht in a Thai bank account? If so it is normal for immigration to check that you have honoured the requirements for your current extension and you will fail this check if you didn't have 800k baht in your account for 3 months after obtaining the extension and never going below 400k baht at any point during the year, that's why people get stuck with agents. Usually the only way to get out from under the agent is to leave the country and start over. But let's assume you did have the money in the bank...
Will you have a full 12 months of a minimum of 40k baht each and every month at the time you will apply for the next extension? If not you can't use monthly income as the US embassy won't certify your income. If you do have the full 12 months will your local immigration office accept monthly income? An increasing number of offices will no longer accept that for an extension based on marriage.