, because the British embassy in Thailand wouldn't issue an income affidavit. You are in a different situation from the OP's. Please check Tod's comment.
, That totally depends on the country that issues the passport. Some countries void/invalidate the old passport at the time of issuing a new passport. Some do at the time of the new passport application.
You use a new passport to both leave Finland and enter Thailand.
Make sure you show the old passport together when you enter Thailand, and be sure you are stamped in a new passport based on the re-entry permit in your old passport.
Once you are back in Thailand, bring both passports to the immigration office that issued your extensions to apply for the transfer of stamps to the new passport.
, as I wrote, some offices are not happy with pdf ver even if it stamps by bank. They want a bank printed transaction history. Better to check in advance.
, not all immigration offices accept the PDF version sent by email. Some allow only bank printout versions, and some accept PDF if it's with an actual bank stamp. You better check with your local office what versions they'd accept for financial proof.
, It depends on the office. If your local office is CW, bank letter and transaction history can be up to 7 days old, along with the bank book updated on the day of application.
You (every foreigner, regardless of what type of visa/entry) need to submit TDAC, the application window is from three days before until you enter (are stamped in at passport control at your entry point to Thailand).
So, you are going to apply for an initial in-country Non-O visa based on marriage to a Thai male. You can apply for it anytime now, as long as you still have
*****
days (depending on your local office) remaining with your current stamp.