You can find some good infos here:
Hillstream Loaches - The Specialists at Life In The Fast Lane — Loaches Online
On the other hand, I'll be updating my blog on them as well:
My Little Underwater Eden
just posted some infos of the water parameters of one of their natural habitats
I would say that this loaches are not suitable for the ordinary tank. They are high oxygen demand loaches living in fast flowing streams. My experience so far, they can be kept in groups, a little territorial especially adults, but not to the extend of killing each other, I don't think they can anyway :)
hardiness/ease to care? Quite easy if they are kept in the recommended tank setup...