It’s illegal to hold anyone’s passport as a passport is government property. Keep this in mind when anyone (except an authorised body) takes your passport for several days.
Why do you need to transfer money here for “tax purposes” considering you don’t live or work here? This may be one of the reasons as to why Thailand is blocking all accounts that are laundering money. To answer your question, yes, you need to get a long-term visa (non-imm or elite) if owning a bank account in a country that you only visit twice a year is very important to you.
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