Yes, Gionee X1 does have a fingerprint sensor, which is located on the back side of the phone.
Yes, Gionee X1 does have a LED flash for the selfie camera.
No. Gionee X1 has 2 dedicated slots for the Sim cards and one dedicated slot for the memory card. You can expand phone memory by up to 256GB with the help of the MicroSD card.
Yes, with the help of App Clone functionality, you can use 2 WhatsApp accounts in Gionee X1 at the same time.