(1) is as others have pointed out a recent/current definition, not one for all time: the original "terror" was carried out by the state and we still refer to a "reign of terror"
(2) Political policy? Or the behaviour of society as a whole?
(3) No. The definition must ALWAYS be fluid and open to dispute. Otherwise it's too easy to hijack
(4) "If you kill 1 of us, we'll kill 10 of you" That's pretty much what happened at Oradour and I really have some difficulty in applying the label "terrorist" to the resistants who killed a German general and not to the "state actors" who killed 600-odd men, women and children.
Terrorism is the use of terror, i.e. deliberately harming/killing some innocent people, or forgetting completely about proportionality, or imposing extremely brutal collective punishment, in order to make sure that others don't even consider arguing with you, or to make them give in to your demands. With this definition, states can't weasel out. For example, "terror bombing" is a phrase widely (and accurately) used to describe so-called "strategic bombing", as conducted by both sides in World War Two.
Trying to pretend that states cannot carry out terrorist acts and policies is a REALLY good way of obscuring the debate. And no, I don't think that's simplistic.
Cheers,
R.