Crits and Magic Damage

I was wondering if critical chance affects magic damage IE staff damage. I want to make an energy rogue and I don't know if I should invest points into Find Weakness. Also, do you think it's better to use a staff or a bow?

Critcal chance only raises the possibility of you hitting a critical.

Critical damage will add on to any weapon you equip. Even a staff.

If you have a staff that does more damage than your bow use the staff.

Find weakness is something I like to use for rogues. Its just nice to have around.