Yeah, the studio already signed the contract to have six movies made.

On the subject on Venom, he's definitely in this movie since they had a clip of him jumping at the camera as the last shot of the Comic-con trailer.

Also, one of my friends gave me some pretty good evidence there will be at least one fight between Spider-Man and Venom. For you see, even in the symbiote suit, Spidey's webs are still that silver color.

In the trailer, they have Venom's black webbing:

trapping Mary Jane

And more prominently, choking normal spidey

Thus, I think they'll introduce Venom probably after Sandman's already defeated and then he'll have one big fight with Spidey. Finally, we all leave the theater drooling over Spider-Man 4.