Yes, one Power Shot per attack action would be fine, but better even to make Power Shot as a standard action, it keeps the flavor of one precise shot.
That means Camouflage and Hide in Plain Sight are totally different things. If You want Your Sniper to be unseen in his gillie, even on terrain that doesn't usually grant that, Camouflage is what You want. Hide in Plain Sight has nothing to do with it, really.Camouflage (Ex)
A ranger of 13th level or higher can use the Hide skill in any sort of natural terrain, even if the terrain doesnít grant cover or concealment.
Hide in Plain Sight (Ex)
While in any sort of natural terrain, a ranger of 17th level or higher can use the Hide skill even while being observed.