The shrimp could have died for a number of reasons. Stress from the previously present Ammonia and Nitrite, stirring up things when planting and replanting, general stress. It's tough to say.
Since you have Tetras and very few places for shrimp to hide, I'm betting it was pestered to death. Would be a good idea to add more moss.
Your GH and KH are perfect for Cherries. No real need to worry about calcium in your tank.