Hi Anna!
I'm pleased that you will visit Viet Nam! So I will give you some suggestions.
As you know, Viet Nam now is very cold. The temprature here is under 20 dgrees so I think you should visit me in March. Near my hometown, there is an airport so you should go here by plane. It is more convenient and faster. When you go there, you travel by bus because it's very cheap and fast. And I think the most suitable accomodation is hotel. Hotels in Viet Nam are usually very cheap. Viet Nam has many wonderful and must-seeplaces. And I think you should visit Ha Long Bay, it is one of 7 new wonders of the world, it is very beautiful. You can see many beautiful caves and stones, which make Ha Long Bay famous.
Now I'm busy so I will write to you later. I hope you'll reply my letter soon!