Grand Moff Tarkin has the following ce:

"If this character has line of sight to an enemy at the start of a phase, you can activate up to 3 characters in that phase. (This can include Droid and Savage characters.)"

2 questions. 1, does he have to activate before using this ability? 2, can he use this CE on the first round if you go first?

No, he does not have to activate first.

Yes, if you go first at the beginning of the round and Tarkin can see an enemy, you may activate three pieces (or two, or one).

Activating 3 first is so awesome against a melee build. Wreaking freaking havoc!

Also a great strategy for tile wars.