The only immigration office where you can do a 90-day report on your DTV entry in Bangkok is the ChaengWattana office. Go to the Government Complex Building B.
, most likely you wouldn't be fined unless the current TM30 receipt is expired (with past check-out) date. The rule is TM30 submission within 24 hours after arriving THAT address, not in Thailand. You can submit it again anytime you want/need to.
If you have a valid TM30 receipt already when you have any application at the immigration office, you would be fine. (unless you encounter any police-involved case)
Your 90 days count is stop when you leave and restart when you enter Thailand again on arrival date as day 1. Your next 90-day report due under your situation is 90 days after your latest entry date.
Yes, that is correct. It's a 90-day entry stamp on a visa waiver (not visa-exempt, it's based on a bilateral agreement) and it's not eligible for tourism extensions. You have until 23:59 on 5 January 2025 to leave Thailand.