I would say the required documents should be your recent utility bill for current location and for freelancer status company incorporation docs along with a signed and stamped letter head stating that you can work from thailand, your personal bank accounts containing equivalent to 500k bt, also you can supplement with your company's statement, previous years tax return, invoices/ledger from from trading account should be sufficient, I know its a over kill but better be safe than sorry. If you are doubtful then you can go for soft power route, just search the group. No one can guarantee visa as different embassies have different policies. Also some embassies demand 500k bt equivalent is maintained through
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/1 month and few are okay with only last balance in your personal bank account.