Short answers, pulled from the story.
The maiden flight of the first prototype aircraft T-50-1 occurred on the 29th of January 2010. Piloted by Sukhoi test pilot Sergey Bogdan, the aircraft's 47-minute maiden flight took place at KnAAPO's Dzemgi Airport in the Russian Far East.
Sukhoi patent for T-50 stealth features cites intention to reduce average RCS to approximately 0.1 to 1 m2 compared to Su-27's RCS of approximately 10 to 15 m2. Combined effect of airframe shape and RAM of production aircraft is estimated to have reduced aircraft's RCS to value thirty times smaller than that of Su-27.
The Su-57 is powered by pair of NPO Lyulka-Saturn izdeliye 117 or AL-41F1 augmented turbofans. Engine produces 9 tonnes dry thrust and 14.5 tonnes thrust in afterburner.
On the 21st of February 2018 two Su-57s performed their first international flight as they were spotted landing at Russian Khmeimim air base in Syria. Three days later two more Su-57s reported to have arrived in Syria.
In April 2002, the Ministry of Defence selected Sukhoi over Mikoyan as the winner of the PAK FA competition. Sukhoi's proposal had itself as the lead designer from the beginning with a joint work agreement covering the entire development and production cycle.