Yes, Vivo India does provide a complimentary protective case inside the Vivo S1 standard packaging.
No. Vivo S1 does not have the 5G network support. It works on 2G/3G & 4G GSM networks.
Yes, Vivo S1 does have a 3.5mm headphone jack.
Vivo S1 standard packaging box contains - Vivo S1, Earphone, USB Cable, USB Power Adapter, Protective Case, Protective Film (applied) and a user guide.