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are located and it will tell you what they need to qualify i wouldn't rely on Google because it very general and can be out of date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
thats not true for a 90 day non O over 50 retirement visa. You have to be in your own country to apply for a Non OA retirement visa which is a different visa
you should have cash from any country doesn't have to be in baht. Very rare they ask but they would not accept a bank card, visa card or what you have in the bank. Has to be cash equivalent