1. Was Zemo's plan really that brilliant?
From my answer to a similar question on Scifi.SE:
I think his primary objective throughout the movie was to obtain hard evidence that the Winter Soldier has killed Stark's parents, in order to turn Stark against the Winter Soldier and presumably Captain America. I don't think he necessarily originally planned to have them meet him in Siberia.
However, as events played out, he eventually decided that dropping the false trail of the inactive Winter Soldiers would likely lead the Avengers there.
The assumption here is that Zemo was able to figure out (or at least had a strong guess) that the accident that killed Stark's parents was really an assassination performed by The Winter Soldier from the Hydra documents leaked by Black Widow. Had he obtained the information he needed from that Russian guy in his house, he wouldn't have had to murder the shrink to get close to Bucky in order to mind control him. (He probably would have still framed him for the bombing of the U.N. though, to draw him out).
2. How did Bucky come back to his senses?
We don't know what his orders were. They could have been as simple as "escape from this UN facility." After he was knocked unconscious from the helicopter crash and woke up, maybe his saw that his mission was a success.
Zemo needs Bucky to team up with Captain America to create the conflict with Tony Stark, so maybe he was instructed to revert back to himself after getting away.
Or maybe it was the water.