Not sure you need to be physically in the US. I got mine all online from the Thai Consulate that was closest to my home address. Your air ticket probably needs to originate from the US.
Wow, Phuket will take a hand drawing but prefer a google printout due to the coordinates on it. When they inspected the hand drawings, the tech actually looked it up on the phone and then wrote down the coordinates for the residence.
Financial requirements is 800,000 Thai baht; that’s only about $23,000 US dollars. You can check on Thai immigrations website for forms and the requirements.
If your son is old enough to get married, he should be able to figure out the stuff by himself. Or at least ask for himself🤪. Even being married to a Thai only allows you to get a non-immigrant O visa, which is good for 90 days.
You can get a visa online thru your nearest Thai consulate. Goggle Thailand E Visa and it should take you to the website.
Once you are here and you rent a place to live, you should be able to get a bank account as you will need some documentation of where you are staying. I found that Bangkok Bank was the most friendly towards Farangs. 
Most rentals will include utilities, if you want good Internet and TV, we use BBB and I like that a lot.
You may wanna keep two cell phones. One for your US phone number and get another one for your Thai Phone. I found AIS to be very good as far as Internet while in Thailand and pretty reliable phone service.
An international drivers license is recognized in Thailand and good for one year. You can work on your tide drivers license later, but it’s not a high priority as long as you have your international license. If you plan a motorbike, make sure your international drivers license is also approved for motorcycles .