To make a long question short, can I displace a unit that's been assigned the Hostage upgrade card in turn 1? Even if I can't, I can do so during deployment (Republic AT-RT), correct?

You can do so. The unit is immune against enemy card effects, which displacement isn't. I have wet dreams about panicking the enemy hostage unit into my direction in round 1 😁 . Not easy to achieve using displacement only. But with war weary and maybe a creature trooper stomping on it twice (thrice with new ways to motivate them) during first activation 🤔 .

1 hour ago, SailorMeni said:

You can do so. The unit is immune against enemy card effects, which displacement isn't. I have wet dreams about panicking the enemy hostage unit into my direction in round 1 😁 . Not easy to achieve using displacement only. But with war weary and maybe a creature trooper stomping on it twice (thrice with new ways to motivate them) during first activation 🤔 .

Hard to do as you can't displace the leader or your opponent can move the unit in a favorable direction.

46 minutes ago, Mokoshkana said:

Hard to do as you can't displace the leader or your opponent can move the unit in a favorable direction.

Not that hard. You get to do the turn 0 hostage move and thus the cohesion placement. Line up the non leader models so you can run them over one at a time without touching the leader.

Units get +1 courage which means they need to be displaced 4 times before they would panick. This is going to be difficult. Even if you manage to double displace them with two units, they would still only need to roll one suppression off to get an action. Also, if they have a Courage 2 corps, you'd need 6 displacements. Am I missing some trick?

Oh, I forgot that they get +1 courage. But that makes my dreams even more vivid 😂