Have a look at this. It explains the motor bike situation much better than I can.
https://vietnammotorbikerental.com/v...riving-license
Also note that the "road rules" are regarded by locals as more a set of loose guidelines, mostly to be ignored. So don't expect vehicles to actually stop at red lights or to give way. Vietnam takes the term "defensive riding" to a whole new level. You will also quickly realise how useful the horn is. Pedestrian crossings are simply some interesting white lines painted on the road.
All of the places you mentioned are worth a visit. I can recommend that while in Hà Nội you stay in a hotel in the Old Quarter.
My daughter-in-law is from Hà Nội (lives in Australia with my son and grandsons) and I visit her parents regularly. When I am not staying with family I have stayed at the Bodega Hotel at 133 Hang Bong Street Hoan Kiem District. You can get a 1 bedroom standard double room, with breakfast and no credit card fees, for A$26 per night. I have also stayed at the Hà Nội Holiday Diamond Hotel, 5 Nguyen Sieu Street Hoan Kiem District. A$41 per night will get you a standard double or twin room that sleeps 3 and breakfast.
The Bodega and the Holiday Diamond are within easy walking distance of all the main things to see in the capital. I can recommend a visit to "Bia Hoi Corner" at the intersection of Ta Hien and Luong Ngoc Quyen in the Old Quarter. Bia Hoi is fresh beer tapped from barrels and will cost you around A$0.25 for a large glass. Sit on plastic stools and watch the street culture.
It is worthwhile booking your transit from Nội Bài airport into the Old Quarter through the hotel where you choose to stay. It will be much cheaper than a normal taxi and you won't get ripped off.
Tận hưởng chuyến đi nhé! Enjoy your trip!
PS, you are thinking of Phong Nha-Kẻ Bàng National Park. Again, well worth a visit.