Details. Which Muay Thai camp, how long was your 500k sitting in the bank, is it a normal personal bank account in your name, how many months bank statement did you provide, were you asked to prove location and how did you prove it, was there any further documents requested? How old are you?

Answer each and every one of those questions in detail.

3 items need to sync between phone provider and bank, your account/passport name, your phone number, your passport number.

Are you asking about before the application is submitted or after the visa is approved?

Regardless it's each individual embassies policy how long the money has to be seasoned before the application, but after the Visa has been granted there is no actual rule about how long it has to stay in the account.

You aren't going to be getting a work permit if you have a DTV because you can only get a work permit on the NoN O marriage or a non B.

Number of DTV applications are rejected for various reasons and there's nothing stopping you from resubmitting your application with sufficient approvable info. That said, using the proper school with the proper documentation and the likeliness of rejection is extremely low.

No seasoning requirement for UK applications

It's only an intended or proposed date, you are not bound by any flights or dates

Just ask Google or chatGPT

If you have your own business then choose the workcation category. Draw up a contract, and employment certificate hiring yourself and authorizing yourself to work remotely in Thailand. Likely need to submit at least 3 months of personal bank statements where you can highlight your income maintaining balance of the 500K funding requirement.

Once issued the visa has a use before/validity date. You have until that date to enter the country, and then you will be stamped in for however long the visa allows for. For most visas you have 90 days from date of issue to use/enter the country.