Just a quick question about the mechanics of these two. If I attack Vader allows me to take two damage to inflict a critical but says nothing about hitting. Does this mean I could potentially activate Vader twice in the same round of attacking. Once after the first attack and again if I miss and gunner activates

Cheers

Yes, that's correct.

You can even use Vader when you have 1 or 2 damage cards left before dying, kill your ship, then use Gunner. But if you do that, you can't use Vader again after using Gunner.

You can use Vader as long as you are "alive" while using him. I'm not sure if it possible but you could even use him more times in a round if you could make even more attack.

That "being alive" thing is in the FAQ where they say Vader can be used only if you have hull remaining on your ship. Now strangely Hull is never decreased as you take damage but it is accepted that the FAQ is saying you couldn't have an attack miss triggering Gunner (because of the miss) and Vader (because of the attack) then use Vader (killing your ship in the process) and use Vader a second time with the Gunner attack which you'd still get despite being on a doomed ship.