It's his non-leader "leader" zeta, and the best one to do first.
Personally:
1 - CLS "It Binds All Things"
2 - Han "Shoots First"
3 - Chewie "Loyal Friend"
4 - TAC "Chewie's Rage"
5 - Old Ben "Devoted Protector"
6 - CLS "Rebel Maneuvers"
7 - Old Ben "If You Strike Me Down"
The rest can be applied as needed. You might rank Raging Wookiee up there, because being immune to ability block and cooldown increase can be pretty handy depending on who you're fighting.
I'm recommending both on Old Ben because if he's tanking as much as he does with #5, he'll most likely go down and you'll want #7 when he does.
As for Guard: set it up on CLS for sure.