What is the process for UK expats to obtain a Non-Immigrant O Visa and its extension in Thailand?

My husband and I, from the UK, are expatriating to Thailand, we’ll also be using it as a base for travelling around SE Asia and Australasia. I am 51 years old and my husband is 63, we would both ultimately expect to attain multi-entry Non-Immigrant O Visas, mine as a trailing spouse and his for Retirement. This, we understand is the simplest and cheapest visa option for us.

My question is around the timing of our annual extension date. The only time each year that we can say with some confidence that we would always be in Thailand to present ourselves for our visa extensions is mid-January so it is our current belief that we should try and co-ordinate our 1st 12 month Non O extension to be done on say 18th January 2023. Working back from that we would apply in Thailand for 3 month O Visas to commence 18th November 2022, having arrived in Thailand on Visa exemptions up to 30 days earlier. My Husband would place 800,000 THB in his Bangkok Bank A/C before the beginning of September 2022 and hold it at that balance at least until 18th January 2023.

Will we need health letters from our UK doctors and/or criminal records checks from the UK? We will both be attaining health insurance in Thailand, will it need to have an annual renewal date of 18thJanuary to coincide with the required visa extension date?

Is the above too elaborate and/or incorrect or could our process be simplified please?