I never used to have a problem withdrawing or transfer big amounts, until last month when I wanted to pay my yearly rent. I was unable to transfers 100'000THB to my landlord and got a notice to come to the bank for ID verification if the amount is 50'000THB or more.
The daily withdrawal limit is determined by yourself but the individual transaction limit is determined by the bank. If you set your daily limit to 100'000THB and want to withdraw that amount, then you just do it in four transactions. Of course that will cost you four times ATM fees too.
Before you exit Thailand, you need to get a re-entry permit otherwise (depending on the visa you have) your visa or extension of stay expires the moment you leave. That doesn't add any additional days to your visa or permission of stay.
You can stay away as long as you like, as long you return within the validity of your visa / permission of stay.
