How long do I need to stay in Phuket before moving on after arriving on a retirement visa?

Better to get your Non Imm O visa from the RTE London, much easier than in Thailand.

Or better is direct to ask in you country fir a retired visa ... if they give it at the moment

Well never the less , the plan is to open 1 July for all double vacillated virus free tourist, so go to the next consulate and buy a 60 days tourist visa witch can be extended again for 30 days , sob you will have 90 days . Only direct flys are allowed . So check the airlines , in Phuket you need to open a thai bank account and depot 800 ooo thb to month before you ask fir a retired visa . Try kasikorn bank they are easy . You need address on phuket , a rented apartment. At the moment very cheap , or your hotel will give you a letter that you resident there .

Best bet is to wait for the government to announce the opening of the "sandbox" and the conditions associated with it. Anything else is proposals and speculation. I certainly wouldn't be booking any flights, unless you're prepared to wait months for a refund.

If it does go ahead you have to spend 7 days in Phuket then you can travel around Thailand. But that is a big IF as I can’t see it happening either.

Agreed.

I really wouldnt count on the Phuket sandbox thing happening in July. This plan was made before the current wave of infections.