My theory about #1 ties in with #6. I think Castiel found out whatever it was that Chuck saw at the end of tMatEotB, the thing Zachariah told Chuck he wasn't allowed to tell Dean and Sam, and Castiel was going to give Dean warning. And that's what caused the angels to drag him back to Heaven. He was going to disobey.

He'd skirted the line before but not actually crossed it, but if he told Dean something that 1) was interfering with the prophecies and 2) something which was forbidden to share with the Winchesters, then that would be Bad. As Anna said, disobeying is angel's murder one.