Vietnam Travel money advice

My dad and I are taking a holiday to Vietnam this weekend… I’m wondering how Many American Dollars will be useful, and where the best place to exchange NTD to Dong and USD is. I usually just pay the exorbitant fees at Taoyuan and live with it, but my dad has a lot of opinions.

I read that USD is sometimes preferable to the Viet Dong for small purchases and “deal breakers” when bargaining.

Any travel tips are also appreciated. We’ve got ten days. 3 in Ho Chi Min, a couple in the central coast (An Hoi, i think) and a few in Hanoi. I hope to see the usual wonders, but I’m open to off beat ideas as well…