Start with the capital, move into limestone countryside, spend a day among the bay islands, then continue to a trading town and the southern metropolis. This is an introduction for someone who enjoys changing surroundings. It leaves two full sightseeing days in each city and in Hoi An, with one full outing in Ninh Binh and one on Ha Long Bay. Arrival afternoons are smaller, and both flight days end with dinner near the hotel.
Book three nights in Hanoi, two in Ninh Binh, two in Ha Long, three in Hoi An and three in Ho Chi Minh City: thirteen hotel nights altogether. Day 14 is departure. Both Ha Long nights are ashore; this plan buys a day cruise rather than overnight accommodation aboard.
The price of this variety is four hotel changes. Two involve flights, with road journeys at both ends. If packing every few days sounds tiring, remove a stop and distribute its nights among the others before buying transport. The itinerary below deliberately keeps mountain trekking, island stays and a Mekong overnight cruise outside the fortnight, so the listed full days remain usable.