Now what I want to know is, what happens when you roll a natural crit? Does Greedo have any effect? Say you roll hit/crit. That would be 2 crits right?

Yes, because you deal cards one at a time starting with the ones caused by (boom) results, so the first card you dealt would be face down, and Greedo makes it dealt face up.

Low PS would be better, so you can clear shields before he activates.

You still take the crit when you defend, even if you have attacked and dealt a crit already, because it says AND, not OR.

Yeah, that's how I read it. You have the chance to dish out a crit or take a crit every round.

Now what I want to know is, what happens when you roll a natural crit? Does Greedo have any effect? Say you roll hit/crit. That would be 2 crits right?

I don't think we're seeing it the same way... You put him on Boba, and he deals one damage card to an enemy Y-wing. That damage card is dealt face up. Your enemy is fielding Kavil, PS7, so he would fire next. Kavil deals one damage card to Boba via an Ion Turret. Boba must still flip this card face up, even though he dealt a crit previously via Greedo.

Both times count. You still take a crit even if Greedo affected an attack you've already performed. Therefore, low pilot skill is preferred, because you're going to take that crit regardless, and you want the enemy to be out of shield before you fire.