I have done four extended tours in Vietnam, one of the best places in the world for bicycle touring. I find the roads, even in the city, extremely safe as long as you follow the basic rule which is you worry about what's in front of you and remain consistent and stable in your riding. Traffic efficiently flows around you at that point. Since there are so many users on the roads, from pedestrians, farm animals, millions of scooters and automobiles, everyone is hyper-aware of other users and adjusts accordingly. Accommodation is plentiful, and the only real option tenting really is not an option there and is not recommended. Food providers are everywhere, but the quality is very hit-and-miss. You definitely never go hungry, regardless of your destination. If it is your first time there, I would recommend starting in the Mekong Delta and getting acclimatized to the rhythm of Vietnam before heading north. I would recommend staying away from the big tourist hubs such as HoiAn, DaNang and focus on the rural regions.