8 players hasn't been confirmed yet, its only a rumour base off what the studio head at Treyarch said. If they do place 8 players into zombies, they will have to expand the maps, create 4 new characters in zombies, and much more. If they do add it, it'll be cool, but it is just a rumour yet.
Well as they're using the Multiplayer engine for zombies now instead of the story engine, i'm pretty sure the can put 8 players into one game, also with the multiplayer engine they're able to make bigger maps, from what i have been reading the maps will be 3-4times bigger than moon
There wasn't; During Blops 1 there was a viral marketting campaign by Treyarch to leak details about zombies returning, they used the website gknova6.com (is still working now actually).
Since they just came right out and stated zombies was back this time thought, I really don't know if there will be a trailer or not, but if there is, it will most certainly be just before launch; Treyarch tend to focus on the campaign in their trailers until just before launch, then show MP.