No. Vivo S1 does not have Qualcomm Snapdragon processor but it has latest the latest MediaTek P65 octa-core processor.
Yes, Vivo S1 comes with 18W fast charger in the box and the mobile has fast charging support.
No. Vivo S1 does not have a notification light but it does have Always-on display.
No. Vivo S1 does not have the front camera flash. It has a display-screen flash.