Each embassy sets their own requirements. Unless someone else has tried using the exact same paperwork as you at the exact same embassy, their information will not be of much use. The embassy decides what they will and will not accept.
There's no such thing as a permanent visa. Owning an apartment doesn't mean anything for your ability to stay in Thailand. First you must qualify for a visa, then you must apply for it and maintain those requirements, and most likely you will need to apply for an extension every year. The only people who don't need to maintain visas are permanent residents (must be married to a Thai or have a job in Thailand for multiple years) or Thai citizens.
I don't know anything about the process of getting a Thai passport.
Most of the Thai embassies in the US have a processing time on their website listed as "up to 15 business days"
You absolutely have to wait until your mother has her passport in order to apply. You can't apply for a visa without a valid passport, and the visa itself will have the passport number and passport information on it.
You don't have to drive anywhere for the visas. All Thai visas in the US are done online via the e-visa system. You'll still apply through the LA Consulate though.
this only an option for the 2nd annual extension. You cannot use monthly transfers if you plan to apply for a 90 day non-O visa in Thailand, and you cannot use monthly transfers for the first 1-year annual extension based on the 90 day non-O visa. Even if you already have 12 months of transfers completed before you go to Thailand, it would not matter because the ONLY options for the non-O visa in Thailand and the first 1-year extension are embassy certified income or 800,000 in a Thai bank.
No, he would be denied extension for failing to meet the requirements of the previous extension. Those requirements very specifically say you must keep your bank account at 800,000 baht for 3 months after you receive your extension and never let it drop below 400,000 baht at any time.
If the agent puts the money in his account and then removes it, when he goes to immigration next year he cannot provide a bank statement that shows he met last year's requirements and they won't care about this year's extension at all, he will be denied straight up and immediately for failing to meet last year's requirements.
Then he'd be required to use an agent again next year because he can't show a 12 month bank statement that shows he met the requirements this year. Then the cycle goes on and on paying an agent every year
2) The consulate doesn't dictate immigration policy. Immigration is a different government agency.
Proof of onward travel is not normally asked for by immigration when you enter Thailand. But it is often asked for by your airline before they let you board your flight. So you need to check with your airline what their policy is for people flying to Thailand without a visa.