check how you booked your flight. I have travelled many times with thai airways and if you book and checked in to phuket then its as I have said you go to transfers sometimes yiu can do immigration at transfers of at destination just depends on how big the airport is
If you booked all through thai airways then you dont go through immigration in bangkok you go to transfers this will take you to your next flight the phuket. Your bags if checked in at uk to go to phuket then your bags will be in phuket as you arrive. You will go through immigration at phuket Airport
ThrillingKoala6126 best log on to the e visa website where you are located and it will tell you what they need to qualify i wouldn't rely on Google because it very general and can be out of date
for your first year extension it has to be 800k baht in a thai bank account, for 2nd and ongoing extensions then you can look to switch monthly income method as long as you can show 12 months of income at or above 65kbaht in your thai account