I have a few questions about said combination:

a) can i use vader twice in one round?

b) if i kill myself with vader, can i use gunner? If so,can i use vader again?

Regards

a) Yes you can.

b) You can use gunner, but not Vader again.

It's in the FAQ.

Thank you Sir

That is not what I read in the FAQ. Under the Card Clarifications section, on page 14, the Darth Vader crew card is discussed. It says that if you attack twice in one round (ie with a Gunner) you may use Vader after the first attack. Since Gunner triggers a second attack and Vader triggers on an attack, it would appear that you could use Vader again. The FAQ only specifically addresses the case where after using Vader on the first attack your ship is destroyed, do you get to make the second attack triggered by the Gunner. The answer in the FAQ is yes.

That is not what I read in the FAQ.

The very first sentence means that you cannot use Vader if you are already destroyed.

Attack, miss, execute Vader, Vader destroys his ride. Without the FAQ the ship would be removed from play right now. With the FAQ, gunner attacks. After the gunner attack the ship is removed from play.

Oops. Have to check all of the conditions first, if you weren't destroyed then yes you could use Vader again but that wasn't the question. My mistake.