Hi Travel Guest,
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Your itinerary looks pretty damn good to me as an introduction to Vietnam (with an Angkor Wat sidetrip). I think you were right to remove Hue - not only because it would be too much, but also because it's a sh!thole of a city! Nothing much to see at all... move on by!
Hoi An is an absolute gem of a town and I wonder whether two days is long enough... it's a wonderful place to laze around. There's a restaurant there called The Mermaid... check it out. Wonderful food - they do a couple of Hoi An specialities... I forget what they are! But just ask the friendly staff. Also be sure and hire some bikes and cycle to the beach at Hoi An. On the way there are a few restaurants that sell fresh crab in Tamarind sauce... divine! Cost $3 although that was four years ago now... adjust for inflation...
Definitely get in a side trip to the Mekong Delta (maybe down to My Tho and stay overnight), otherwise four days in Saigon is going to be too much. It pales in comparison to Hanoi, which oozes colonial charm and is a joy to get lost in.
Have a great time - and let us know how you get on and if you have any recommendations as a result of your trip!
cheers,
Steve