Current guidelines would suggest you will be given 7 days emergency extension to get out of Thailand. However, the guidelines also say if you can convince the IO that you are a genuine tourist then 3 entries visa-exempt is OK. Please report back of the outcome.
Anonymous participant I applied in the UK and although they require 3 months bank statements they only require the 500k to be in the last month, so I transferred 500k from my savings. Nothing strange about it.
. This is only a rule for visa-exempt entries as all other entries, apart from VoA, have already satisfied the financial requirements with immigration when obtaining their visa. Whereas visa-exempt entries are unknown tourist. I've been coming here for 20 years and never known anybody say different. I have a DTV which is a tourist visa and the 20k is not a requirement.
I haven't heard any reports about Hat Yai, so I look forward to your experience there. Make sure you print off your DTV and hand it in with your passport. No need to print your TDAC.
It is not random. The people who get checked are suspected of not being genuine tourists, so they get selected for secondary screening. Usually people with a history of staying long-term in Thailand using tourist exempt-entries and border bounces.
Setup a company with you as a sole director and give yourself permission to work remotely in Thailand. Show income tax statements. You don't need contracts as your bank statements show your monthly income. This is what I did in the UK and it worked. It is a lot more difficult as a sole trader/self employed