Going from Luang Prabang to Pakse is a bit of an effort but very doable. Check out how to go from Luang Prabang -> Vientiane -> Pakse. Its only a 23 hour excursion ;)
Laos isn't the easiest place to eat vegetarian, but when you know the right places to look you'll find a lot of delicious food here!
Going from Chiang Mai to Luang Prabang is a long 3-day journey, but this article will guide you every step of the way :) Using the slow boat on the Mekong is a must do!