Potency. there is some discussion that maybe CB. but not DC as our individual spells aren't that powerful and DC doesn't do as much for proc triggers.
Crit Bonus imo, but I try to keep my potency to a certain level (atleast 300 static solo) so I mean, it's your call really, but since chanters are melee mages I would say CB for most things. and never Double cast since it's so bad
you should keep them both about even but for an illy you're probably better off going slightly higher on CB because it affects pretty much every modifiable proc, were as potency only affects a few.
yes, both critical bonus and potency affect most all combat arts and spells but potency only affects a few select procs and critical bonus affects all modifiable( potm, arias, stampede,ect) procs. also auto attack should be a substantial source of damage on your parse on most fights. keep them even or CB slightly higher, it's what i do anyhow and my chanter's damage improved after i moved away from full potency adorns.