I would start in Hanoi, end in HCMC, then fly over to Siem Reap. I suggest going north to south to help you acclimate to the weather. Going the other direction also works if it helps your flight situation.
Domestic flights are relatively cheap, so I recommend taking buses for short hops and flights for medium/long hops.

Look into Phú Quốc or Con Dao islands. Beach-wise I would skip Mũi Né/Phan Thiết.

Culture in terms of history is more north. Saigon is the modern culture and melting pot. I'd agree with starting in the north. If the two weeks is including 3 days or so for Siem Reap, then you might just want to focus on northern and central Vietnam and leave Saigon and the Delta for another trip someday.

I'd start with flying into Hanoi, 2 or 3 days there, then look at the options of Sapa and the far north, Ha Long bay, and Ninh Binh. All of those require two days in my opinion. (Some people will consider them very interesting, some will think it's touristy. Truth is you can make it more or less touristy if you go to the main places or you go to the same area but the less popular places. I like all of them.)

From there I'd move into the central area. Hue, Da Nang and Hoi An. More culture history and sight seeing. Look into the Cham minorities and their history in this area too. Can do the beach in this area too.

If you like those options, your time would be about up. You can fly to Siem Reap direct from Da Nang if I'm up to date.

If you still want to fit in more, you could opt for a beach at Quy Nhon or Nha Trang, or do Saigon and the Delta to finish up.

Are there any restrictions yet with regards to arrivals from China, I'm supposed to be stopping one night in Shanghai on my way to Hanoi in a few days time?

No restrictions yet. Monitoring arrivals in the main airports as I understand. First two confirmed cases in Saigon Wednesday (1/22) and two suspected in Hanoi, so I suppose things could change and you should keep checking news sources.

Thanks.

Two questions please guys, I’ve had to extend my stay in Vietnam by 2 days so as to meet the entry requirements for Singapore, I transited Shanghai on the 28 Jan.

Firstly, I think the date on my passport is wrong, it’s says leave by the 12 Feb. Essentially the 15 days didn’t include my day of arrival, will I have issues using this as the day I leave?

Secondly, what are my options if I arrive at the airport on the 12th and find my flight cancelled and am unable to find another flight?

I count 12 Feb as 16 days after 28 Jan. But nonetheless the date written in the visa stamp has always been the date you have to leave. I suppose you could try to get them to amend it if that's wrong, but the issue is bureaucracy/language/interest and figuring out where to do it.

That being said, I had a mixup once with the immigration agent stamping me in on a multientry visa near expiration, rather than the new visa on the next passport page good for 90 days. I was remiss in not checking until my exit 80 or so days later. I was nervous, and the guy at the counter was unhappy on exit immigration but didn't speak English. He took me to a supervisor and he was able to understand the issue and stamped me out. It seemed like they were very understanding. YMMV.

Your second question, there are obviously many flights at the large Int'l airport. More a question of if you're willing to pay to go somewhere and what passport you have. Otherwise there's always the bus to Cambodia. Very cheap, several hours to get to PP.

Answering my own question, there were no issues clearing immigration is Da Nang today even though the wrong date was on the passport.

I'm living near Hoi An in VN, and am loving it.

I do struggle at times not speaking Vietnamese but I am happy with life here overall.

Tell us a bit more about life there. We visited Hoi An last year I think it was.

Trip on mid march trip
 

Group of 8. Half are up for it half feat coronavirus

any thoughts appreciated

I will share with you my recent experience and let you draw your own conclusion whether you feel comfortable visiting under the circumstances.
I returned last night from a 2-week trip that was pretty much evenly divided between Ho Chi Minh City, Dalat, Nha Trang and Hue.
General observations: People are wearing face masks more than normal, causing some supply and demand issues. The irony is at certain tourist locations, they were handed free (one per guest). Hotel/restaurant staffs and taxi/uber drivers all were wearing masks. Signs posted in hotels advised customers to safeguard themselves against COVID-19 (i.e. hand washing and mask). The traffic is definitely lighter in the above cities, especially in Nha Trang where the tourism business was highly dependent on visitors from China. On my last evening in HCMC, the Nguyen Hue pedestrian street area was jammed pack with people out enjoying the weekend, many with masks but also saw quite a few without.
Personal thoughts: I never had any serious concern about the virus situation during my trip. However, I followed local and international news twice daily to keep up on the situation. I practiced hand cleaning more often than I ever did in the past. I packed a bunch of regular and N95 masks with me and never went out without a couple in my pocket. In close area such as airplanes, taxis and hotel elevators, I do wear mask.
In summary, I had a very good time back home, as usual, and I did not let myself be overly affected and even panicked by all the news from the region.

I was suppose to hit both SIN and DAD. I decided better safe then sorry. Now had either Country not have any deaths or people who had CV and if those Countrys werent visited by tons of Chinese then I would have thought about it. Being both places had active cases and tons of Chinese tourists, I decided its better to push off then trip till the All clear message is posted.Also it would have to be where the citizens dont flock to China as well

Just came back from Vietnam yesterday. Hilight of the trip:

My local Vietnamese friend's unknown occassional abdominal pain was OK prior to going to Tam Coc. On that evening of the day that we got to Tam Coc, her pain started to get excruciating to the point where she couldn't sleep. Took forever to find a cab (Mai Linh) at midnight in Tam Coc and it was by fluke. Drove to Ninh Binh General Hospital. No Emerg dept in sight? Wandered into ICU ward and ICU MD stated to my friend that she probably needs an endoscopy done but no appropriate staff (specifically GI) until morning. No way in hell was I gonna wait as appendicitis popped in my mind.

Same cab driver came back to pick us up. We decided to get back to Hanoi and cab driver agreed to get us there for 1200000 VND. Drove back to hotel in Tam Coc. Packed our belongings. 90 minutes and 89 km later, we were back in Hanoi. Gave the driver extra 100000 VND. Friend ended up being hospitalized and admitted for a few nights. Gastritis was the Dx.

Even though this was unexpected, try not to get sick or ill while in a small town/city. Resouces are next to none...and can be a scary situation.

All in all, 18 hours in Tam Coc instead of the planned 3 days. I will definitely go back there.

Is it the rainy season in May in Vietnam? I plan to do a Halong Bay cruise in May.
thank you for any advice.