obviously depends of visa you have if you are here on retirement visa you should not have such number as you are not allowed to work here hence you should not have any tax liabilities if i am right ....
she can get a dependent retirement visa on yours this is what my wife got when we moved here from aussie similar ages to you when we applied she can switch to independent retirement visa once passes 50
if you are in phuket u need to contact them in bkk i used my local law firm to make contact and sort out for me this was 3 yrs ago but i think you need to travel to bkk to finalise once approved with passport as two of my friends did recently xx
i think u need min 800,000 but a period after issued u allowed to use some of this but u must always maintain non 400k at anyone time ... maybe things changed but that was last time i read abd the 800k must be in bank minimum 3 months prior to obtaining your extension so if extension due april and i only have 400k in bank u better top it up to 800k and they will check asper your bank statements so it’s 11 jan now so u would only be able go for extension after 11 april if u top up now