I have stayed in Hue for almost 2 weeks. There's so much things to see in the city. If you haven't tried going to Tam Giang to sunrise or sunset, both are amazing. They have the Bach Ma National Park and Elephant Spring as well. If you are a little adventurous, you can check the abandoned water park. Hue Festival is being celebrated around June. I guess what you meant was the independence day celebration and yes, it is a big thing as well. They have several activities since it being followed by another holiday, the labor day observance. All my travels in the city were from the same company, they are called VM Travel. They were all nice and even bought me a cake when they've learned that I was travelling on my birthday. I took the train from Danang to Hue, I had to fall in line to get my ticket, but you can always ask assistance from travel agencies to secure you seats most especially during holidays. This is their website: vmtravel.com.vn