Dujiangyan is just a really nice place in general, but I’d be sure that you’re interested in Chinese culture and Chinese people in general before committing to a place like that. It sounds like you already know the important things though – it’s a beautiful place without much of an expat community. You won’t be far from Chengdu, but once you get used to the luxuries of Chengdu, it can be tough to live in places like Mianyang or Dujiangyan unless you’re really committed to one or more aspects of Chinese culture. With the bullet train Chengdu is never far off, though.