if you extend the visa stay in Thailand you definitely will need to show the funds, if you leave and re-enter Thailand to get a new 180 day stamp there is a low possibility they might ask.
Overstay of less than 24 hours when leaving by an airport will not get you a fine but you will get a stamp that says overstay less than 24 hours fine waived. It will not affect applying for the visa, but it's recommended you don't overstay.