I've seen snippets of the most recent livestream, but from what I can tell you have to 'manually' take cover (ie you crouching and putting stuff between you and the bullets/shurikens/choppas) but devastators (and Im guessing other heavy-weapons infantry) can 'mount' their weapon on cover for benefits (this was covered in an earlier ITW iirc).
They said there would be some Gears of War type cover mechanics where you can vault and auto slide or move to nearby cover but I haven't seen any of that yet because it's still in Alpha.
Yep, unfortunately it's a NO NO. I had made a similar thread a long time ago about small interactive objects like crates, barells, sand bags that could be used to create make-shift barricades and the response wasn't positive - basically, too much strain on the servers.
