If in a foreign country then a passport entry stamp and your hotel booking etc. if in your home country then utility bill, bank statement with your address, or drivers license etc.
Offhand I'd say one night is okay, you aren't the typical free visa exempt border bouncer. Altho others with experience at that border might have direct knowledge. Don't forget to fill out the tdac online form for your return to Thailand.
You need to do the monthly payments while on the same visa type to qualify. So bringing the money in on an OA, will not qualify you for the monthly payment method on a O.
If you can prove the remitted money was from savings not earnings before the year you become a tax resident, those funds don't automatically give you a tax liability.