Yes, Vivo Y83 does have the power saving mode.
Yes, Vivo Y83 does have the 2.5D Corning Gorilla Glass display.
Vivo Y83 comes with 5V / 2A charger and it helps the phone to charge quickly.
No. Vivo Y83 has 2 slots dedicated for SIM card and a separate slot for the MicroSD card. You can expand phone storage by up to 256GB with the help of the memory card.