I need some solid answers about T8 elemental set bonuses

[Lightenme]

2 set bonus; Flame shock ticks can be crits.Does this procc clearcasting/elemental oath?

4 set bonus; Is this stackeble? I mean does the previous effect needs to be finished before we benefit again? In other words, if i crit 10k twice in a row, will i still have 200 (8% 10000= 800, 200 ticks evers sec for 4 secs) ticks every 4 secs?

[Spacehamster]

2pc ~125 DPS FS - crits will not proc ClearCasting.
4pc ~350 DPS - Effectively an 8% multiplicative bonus to Lightning Bolt. Behaves similarly to the Mage talent, Ignite. Remaining damage from the previous dot is added to the new one to tick through (theoretically, this accounts for spells in-flight as well).

From Elitist Jerks