I'm still trying to iron out of few of the rules myself but the answers to yours seem semi-clear to me, so I'll chime in.
1) There is no "attacking" allowed during the first full turn. I assume this extends to most varieties of card attacks. But does this also mean that no players may place terrorists in other empires until the full turn is over, even if those terrorists don't attack?
I see nothing in rules that would prevent a player from buying and placing terrorist units during turn 1.
1a) Similarly, does this mean no one can turn terrorist until after everyone has had a turn? Even if they weren't to attack anyone?
I believe the rules say that a player can "turn terrorist" even on the first turn.
2) On the War card, the defender uses the same chart the attacker uses. Does that mean defense depends solely on the size of the defender's development? i.e. there is no accounting for the size of the development from which the attack is made?
That seems to be the case. I've decided that rather than endless rerolls, it seems to be easier to simply have the higher roll "win" the confrontation (either allowing for the attack - as long as it is within the success zone - or neutralizing the attack).
3) Dirty bombs "require a terrorist vanguard." My friend actually reduced a column down to a vanguard to play his dirty bomb because he didn't think the card meant "requires AT LEAST a terrorist vanguard."
It says "at least" in the card almanac. No need to reduce.