The small South Coast Water District has taken key steps toward construction of a $110 million desalination plant, but the agency faces growing questions of whether it’s in over its head for the ambitious project to be built near Doheny State Beach. The project’s ocean-friendly technology has won praise from the same environmentalists fighting a desalter plant proposed by Poseidon Water for Huntington Beach, one of several things that distinguish the south county plant from the more controversial project to the north.