Yes you must get your non-English home country driving licence translated and the translation legalised by your Embassy. There are agents who can assist you for a fee.
In March come in on a retirement visa from the UK Embassy. Use that to open a bank account. Contact an Estate Agent and have a look at the type of housing you may want to rent in the future to give you an idea of what’s available and the market rates.
just about everything you stated is false. Uk does not issue income affidavits. The monthly requirement is 65k not 75k. He will require 800k in a Thai bank account for his 1st yearly extension of stay and lastly moving savings are not taxed.