First overseas holiday - Vietnam?

Hi guys,

Have been doing a lot of reading on this site and the various threads about travelling around Vietnam. My partner and I are mid 20's and have already booked our flights in June/July and will be spending approx. 18 nights in Vietnam flying into and out of HCMC. I'd really appreciate your feedback or tips on what to see and do. Our basic plan was Saigon for a few nights, fly up to Hanoi to spend a few nights, do a junk boat tour of Halong Bay, was thinking up to 7 nights in Nha Trang (we are after about a week of chilling out, beach style) and want to do an overnight/2 night mekong delta tour. Nothing is set in stone - only our flights which leave end of June and back beginning of July.

Any feedback about time frams in each place? Is there another beachy type place to relax other than Nha Trang? Any MUST SEE recommendations?

All feedback is greatly appreciated, we are wanting a bit of culture and aren't wanting to be too run off our feet - being our first overseas holiday and having been together over 6 years this has been a long time coming!!

Cheers.