We are planning a trip to Vietnam with our 4 children ( aged 12 to 18 ) for 4 weeks in January. We want to fly into Hanoi, work our way down by train to Saigon, stopping at the major attractions, then fly home from Siem Reap. We want to do the usual excursions from Hanoi, ie a short highland trek and cruise in Halong Bay, and a boat transfer from Saigon to Phnom Penh.What I am unsure about is whether or not I need to organize these ( and the train journey south ) prior to our arrival, or can it all be done just as easily and possibly cheaper once we arrive? We don't want to waste valuable time organizing these when we get there, but don't want to waste a lot of money by organizing them beforehand. Is January too busy to leave bookings to the last minute? Any advice will be much appreciated!