Yes. Vivo NEX does have the 3.5 mm headphone jack.
No. Vivo NEX comes with 128GB internal storage and it does have the OTG support as well. Vivo NEX does not have the memory card slot.
As of this moment, Vivo has not yet announced anything about 5G network compatibility of Vivo NEX.
Vivo NEX has 8GB LPDDR4X type of double channel RAM. The peak RAM frequency is 1866 MHz.
The Vivo Nex S is a unique smartphone. It looks great, it’s built beautifully, has the best processor you can currently find in a phone and a huge, truly edge-to-edge display.
The Vivo Nex brings some truly cutting-edge technology to the table but does so with an all-too-common mix of familiar failings. Even though we don't think it's the phone you (or we) really wanted it to be, it's still one of the most exciting phones we've seen in a long time.