We basically buy rights for six months, allow the writers to resell their stories for print publication if they choose. I remember stories about that event from Matheson and Bloch. It's whatever seems interesting at the time. Millennial fiction is something I've been predicting for a decade or more will monopolize more of pop entertainment. I'm very proud of him though.
Most people feel that publication on the web is considered first publication.
As an editor I do. It depends on the contract you sign and it depends on how the print publication feels. No private chats, please. I think OMNI still publishes the best sf in the field. Little problem there, I guess.