Is it sensible to enter Thailand on a tourist visa and then apply for a retirement visa while in the country?

as an american there is no way you can show "proof of income" that will be accepted here at the immigration office to get a Non-O visa or a year extension. The US consulate hasn't issued income from abroad notary documents since Dec 31st 2018 :O

That means you have two ways to meet the proof of funds to get a "retirement visa" inside the country you bank 800K baht in a thai bank account in your name only for 2 months before you apply for the year extension

OR

You transfer IN to the country in a thai bank account in your name only from abroad a minimum of 65K baht a month each month every month for the preceding 12 months before you apply for your extension.