all characters' Tweets are written by Jeph. The characters won't follow any "unofficial" (aka not written by Jeph) twitter accounts.
qc twitter posts occur independently of any particular comic or story arc, unless the characters Tweet otherwise.
characters will not respond to @ replies by non-QC characters, so as not to break the fourth wall. Feel free to Follow them, though, since that is the whole point.
don't click on anything Pintsize links. you have been warned.