I am sure you will love Luang Prabang. You can also contact some of our Lao community there in Prabang like @chanmaly and @phetsamone they may have some time. About Vang Vieng I will recommend to take a bungalow on the little island at the north of the town or to cross the river and get a bungalow there as it is quiet. The other side is full of cave and jade water where you can swim, also rent a little motorbike to take a look around it is a beautiful place. Enjoy Laos :)