If you want a "retirement visa", you have to follow the Thai law. And that means 400.
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.000 THB in Thai bank account. And it in fact has indeed to be there over 3 months or live time. That option has nothing to do with actual retirement, but only your age. Which is 50 years, and you are to young.
For a DTV visa you do not need a Thai bank account.
You need proof of a bit of a fortune (500,000 THB) and regular income. Does not really matter if you take soft skills or are working.
Unless that showing pension as income might be difficult.
Picking a random soft skill should be flawless. However in principle you have indeed to (be able to) show every time you enter that you are still enrolled in that course.