You'll like Vietnam.
Go to the Cu chi complex, just for the shit of it. Fun being down in those tunnels. There are two complexes if I remember right, one at Ben Dinh and one at Ben Duoc. I went to Ben Dinh. There will be 2 sets of tunnels, one widened out for gringos, and one that is the original size. I'm a big guy, 6'5", and it was hilarious squeezing into a VC tunnel that a child would have trouble with. Once in a while someone will freak out down there, just tell em to keep moving. Bring a flash light, there are openings down there that aren't well marked and you aren't supposed to go into.. Make sure you get rabies prophylaxis/vaccine before you go, bats like the tunnels and tourists get bit sometimes. There's a "rifle range" there that is more like a carnival; you are well versed in guns so you can probably skip it, but bring ear protection if you do it, the headphones they give you aren't worth a shit and you'll hear everything and get some decent hearing damage.
Ben Dinh is closer to Saigon/HCMC, and if you can, do the tunnels then the Cao Dai temple on the same tour. Cao Dai is pretty neat, it's must just for seeing a weird catholic/Buddhist/Taoist cult that was a big part of their history, especially during the American War. Cu Chi and Cao Dai = one day tour.
You'll get propaganda no matter what, but its pretty laughable, just understand that any tour is going to have "facts" that are far more in line with Hanoi's views than what really happened. RKE talked about the "American Killer Hero" film, its a hoot, especially since the gubmint takes it seriously.
The dong is the second least valuable currency in terms of exchange rate. You'll get something like 33,000 dong per British Pound. And dinner is less than 30,000 dong easy.
Rickshaw is right, if you want a headache get some bia hoy from the Jerry cans. It's a local home brew that is part of Saigon culture but frankly not that good. 333 is decent beer. You'll be able to find beer from other Asian nations like Singha (Thai), San Migy's from the Philippines, etc. Great Pho all around. Cholon in HCMC is the worlds biggest China Town. It looks like Taiwan a bit.
Fly if possible, the roads are styled after the Ho Chi Minh trail and can be a bumpy bastard.
Read up on how to cross the street in Saigon/HCMC or Hanoi. Scooter traffic like you've never seen. Whitey gets killed a lot because they think running across the road is a good idea. One of my best memories is crossing Lei Loi and having to stop on the yellow line between lanes as a bus passed in front of me while eight scooters zipped behind me by less than four inches.
Go to Vung Tao for good seafood.
Hue is a good tour.
If you're going to beach it "China Beach" (My Khe beach) is picturesque. Just up from Da Nang. Touristy and fun. Surf is normal, Decent left right beach break, lots of the accoutrements of beach life. You n the missus can just chill out and drink and eat.
I haven't been up north; a buddy said the north is stiffer, less fun.