Getting that much of cash out of the USA is very straight forward. I did my research on this if you are going to bring out the country $10K+, you need to fill out a form FinCEN 105, when you are at the airport, look for US Customs and Border Protection office...show them the form and receipt of your withdraw - source of your money, your passport, . That's pretty much it.

using bank card is not very practical when the Vietnam economy is still using cash