No. Vivo Y83 does not have the particular LED flash for the front camera but it does have the display screen flash for the front camera.
Yes, Vivo Y83 does have the power saving mode.
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.
No. Vivo Y83 does not have the fast charging support.