If I Crit and that Crit produces Damage over Time (DoT), does the DoT do more damage?
No, DoT effects are completely independent of the hit that produces them. DoTs also do not count as a hit and therefore cannot Crit.
I’ve got 300% Crit Chance, why am I not critting on all my hits?
When a hit Crits, the damage dealt is multiplied by a Critical Strike Multiplier, which is multiplicative with other modifiers. The default Critical Strike Multiplier is 200%. +1% Critical Strike Chance will result in a final chance of 6% (assuming no other modifiers), while 1% increased Critical Strike Chance will result in a final chance of 5.05%. Both stats together will result in a final chance of 6.06%.
Is there a Crit cap?
Technically, there is no cap but most builds gain no benefit from going above 100%, so that is commonly referred to as the Crit cap.
Is there a Crit Avoidance cap?
Yes, this is capped at 100%. You cannot avoid more than 100% of Hits that would be Critical Hits.