1

train times for North to South
For Hoi An to Ha Noi you would need to get the train from Da Nang. I suggest a day train as the scenery between Hue and Da Nang is impressive.

Da Nang To Hoi An about an hour by public transport bus.

Times vary between Ha Noi and Sapa.But usually about 9 to 11 hours.

2

It's not far. About 30 km. from memory.. Very good road.. We took a taxi recently from Danang airport to Hoi An... Can't remember exactly the cost.. something like USD 10.00 or USD 14.00... Takes less than half an hour.

HaLong Bay is located 170 km away from Hanoi, this would take you about 3 – 3.5 hours on bus transfer to Halong city, bus trip normally leaves Hanoi by 8.30 am.

3

lary:
The OP asked about bus to Hoi An, not taxi.

4

Bus from Hoi An to Da Nang can take up to an hour as it stops a lot. Plus it is notorious for leaving late as some friends of mine found ten days ago. If taking it make sure you leave enough time to catch the train or plane from Da Nang.

The train does not leave from Hoi An. To catch a train to Hanoi you would need to get to Da Nang station. The train trip from Da Nang to Hanoi takes about 15 hours but that does vary as some trains make more stops. A day train trip does allow you to see the passing scenery and I have done the trip a couple of times. But last time I looked the times had changed and there were few trains doing this stretch in mostly daylight hours. If going by train try to do the Da Nang- Hue leg during daylight hours as it is one of the great train journeys.

5

It takes about two and a half hours to get to Haiphong from Hanoi by train. There are only a few trains I think. How long the boat to Cat Ba takes depends on the connection and whether you get the ferry, which takes about 3 hours I think, or the hydrofoil, about an hour as far as I remember, though you don't see much. I think you can get to Halong city from Haiphong, though I haven't done it.