Yes, Vivo S1 does have a 3.5mm headphone jack.
No. Vivo S1 does not have the FM radio support.
No. Vivo S1 does not have Qualcomm Snapdragon processor but it has latest the latest MediaTek P65 octa-core processor.
Yes, Vivo India does provide a complimentary protective case inside the Vivo S1 standard packaging.