DPS is the damage per second a weapon does. That sort of explains it all.
You can remove grips and other add-ons, but not runes. To do so you go to the modify armor/weapon stands (near the craft armor/weapon stands).
Things to look for are, is it better than what you currently have on your rogues/mages/warriors. That means both DPS and extras like %attack, and stat bonuses (like +36 magic on endgame weapons), there are a bunch of different effects that weapons can have (bleed, staggering, %heal, critical damage, critical chance, ...) but I suggest you go to a dragon age wiki somewhere to learn more about that if you're willing.
