Religious minorities were treated much better than any other religious minorities in the world here. They sought to convert them into their own religion and those who did not were given 2nd class status.
Janissary was formed by Ottoman Sultan Marad I from captured Christians that were pressured to become personal bodyguard for Sultan. Marad II, his successor still maintained the pressure of Christians into service. The Janissary later formed something closer to a modern standing army and used Gunpowder cannons as firearms to keep attackers at bay.
The conflict between Shia and Sunni was hardly limited to the Savafid Empire since it has been a part of Islam. There was a dispute over who would succeed Muhammad and that is where the rivalry between these two started.