For the physical bond between Venom and Eddie, I'm borrowing a little from the Venom movie in that Venom lives within Brock's body, which makes it easier to feed off the adrenaline like in the comics. And at this stage in their "relationship", Eddie has little control over Venom, and so Venom will appear even if he doesn't want Venom to.
I'm pretty sure combining Ivy and Venom might get you some of the madness that was in RE7. Those were zombie plant people or something I think.
I don't know.
As for someone playing the Gen1's, as I call Stark and all the "main" heroes of the Marvel/DC verse that aren't younger, I'm going to say no right now I'm specifically aiming this RP at playing the younger new generation of heroes so I'd like to stick to that as much as possible.
Edit: As a side note for folks, when I put tagging on there I meant to tag the character not the player So you'd tag Nightwing, Jade, Eddie not their respective players. Just in case, down the line, we have people playing multiple characters so we know which specific ones are in the scene at a glance.