Once you have the DTV that’s it. You have qualified for a 5 year visa. No further requirements, no further schooling, no additional anything. No further payments (Bar in country extensions). There is nothing in the DTV requirement that even requires you to attend your booked Muay Thai lessons.
not true, you can live in Thailand 179 days a year and still get your UK pension uprated. It is indeed tax residency that determines the uplift. Once you lose UK tax residency you lose your pension uplift and state healthcare benefits.
Whether you send your state pension to a Thai bank or not is irrelevant. What counts is your residency. Thai tax residents are not eligible for uplifts in UK pension payments. This is known for decades.