, Non-O initial visa for retirement/being over 50 also has the same financial requirements as Non-OA (banked 800K baht equivalent or 65K baht equivalent monthly). Most of the other Non-O initial visas have their own financial requirements, too.
No, you cannot. At Chaengwattna, you must have 15 days or more remaining with your current stamp (visa-exempt or tourist visa). Now that you don't have enough days remaining, you must apply for a 30-day tourist extension first at the IT Square Laksi Plaza office, and then you are eligible to apply for an initial in-country visa at the Chaengwattana office. You need to check with them whether you can apply for a tourist extension and an initial in-country visa on the same day or not, in your case.
Jomtien standard accepts your extension application when you have 30 days or less with your stamp, but will accept it earlier if you provide a reason on your side.
, unfortunately, no one other than your embassy can notarise your income for your immigration/visa purpose. You need to get your visa outside Thailand to enter on it.
, You are talking about the step when you change the method from the banked money method of 800k baht in a Thai bank account TO a monthly deposit method, not the opposite way (what the OP want to do)
Why not visit your local immigration office to discuss your schedule, bringing your detailed itinerary and confirmed air tickets? In advance or just before you submit applications.
If they can accept, they may complete before your departure. Or they may be able to make the under-consideration period longer.
Even if they say no, nothing is going to be worse than the current situation by asking them.
, many embassies/consulates don't specify the country where your bank is located. Usually, you can use a bank account in any country as long as you can provide the necessary documents at that embassy.