Yes, Vivo S1 has an in-display fingerprint scanner.
Yes, Vivo S1 has a dedicated MicroSD card slot. You can use 2 sim cards and a memory card at the same time.
Vivo S1 has 6.38 inches of AMOLED Full HD plus display. It is further protected with Corning Gorilla Glass 5 level of protection. The mobile has a 90% screen-to-body ratio and has 19.5:9 aspect ratio. Vivo S1 offers 404 PPI of resolution.
Yes, Vivo S1 does have a 3.5mm headphone jack.