The 65k deposits need to start before the first extension is approved so that when it is time to apply for the second extension there are at least 12 consecutive monthly deposits
ff you don't already have one you'll need a Thai bank account in your name only as soon as possible (get a Residence Certificate from Immigration first)
Once you have the original back from FCDO with its attached certified Apostille, they need :
1. The original document(s) to be legalised, certified by FCDO (UK)
2. A copy of every single page including an apostille page from FCDO (UK)
3. Legalisation application form and a copy of applicant's passport for reference (* * Non-Thai can omit this requirement)
4. A fee of £10per documentis required (can be paid by debit card/contactless or cash) ed to be translated. RTE London have a list of "approved" translators in UK on their website
Applications for document legalisation should be submitted to The Consular Section, Royal Thai Embassy, 29 Queen's Gate (Basement) , London SW7 5JB