Is there a reason to take 2 or 3 of the same ability? For example, Cannon: Rapid Fire. If I have CRF 2, will CRF 1 still be useful to me as an extra buff? Do they share the same cooldown timer? In that, if I use one, will it grey out the other?

Yes, it's worth taking more than one.

They have a shared cooldown, but it's much shorter than the cooldown on the individual ability - let's say that you have three officers with it, and it has a 90 second cooldown (just for demonstration). You use it on officer 1, and it triggers a 30 second cooldown on officers 2 and 3. You use it on officer 2, and it triggers a 30 second cooldown on officer 3, and so on.

Ranks 2 and 3 will fire more shots per cycle/space bar press than rank 1, so they're better in their own right.

If you use two rapid fires, one will one the other on a 20 second cooldown. Since it's a duration ability it means you can have rapid fire up 75% of the time if you equip two.

Ah, thank you so much for the answers.

I use 2 of high yield torp. It's super nice. ^^