I'll let you know what I know.

RR = 30%, dDEX caps at 20%, Merits = 5%, Ukko's Fury has a 30% Critical Rate.

That right there is 85%. Rancor Collar is ~5%(90%), Claymore Grip is 3%(93%), Rvg. Mask +2 is 3%(96%), Zahak's Mail/Trophy Legs/N Legs are 3/3/4 respectively (99/100%) Light Earring can get 1% (100%).

100% Chance to crit on Ukko's Fury EVERY TIME? K.

1) Rancor>All
2) No clue.
3) I don't think it works like that. It's x amount of Critical Rate for every x amount of dex you have more than your target's agi.