When transferring abroad, you use the TT rate. So check what they are. If your sending bank is converting to $, what $ will you receive? What would it be if you send baht to your US bank? Usually, the rate is better at the receiving bank.
Depending on your immigration office in Thailand where you decide to live, getting your own visas is probably advisable.
AXA do a cheap insurance that you can reduce further with deductibles, you can also cancel at any time for a prorata refund.
UK embassy said we could use joint account if it had double the amount in it. We each got a copy of our individual statement from the bank for the joint account (Online pdf copy is fine).
If your wife is applying as dependant, she would select Non-Immigrant Type O (Visiting or staying with applicant's family resided in Thailand (more than 60 days)
Where you see the application you made, to the right hand side is a box you can select to view your application, click that which takes you to a page where it shows all stages (pending document check, pending approval and so on). Pending document check is stage 1.
I think Nakhon Si Thammarat immigration fall into the same category. No 90 day under consideration in-country (yes, you have to leave Thailand), no trailing spouse who is 50 or above and last time I did a Non O extension, they required 400k insurance. They also require the 2 months of money in bank for Non O. Not relevant for this chap but maybe for advising others.