HaHa, must type faster
1) No, a broken stand does not lose its ZoC. The only time that a stand loses its ZoC is when it has been contacted by an enemy unit as part of an assault.
1.1) Blocking or covering an Eldar Wriathgate is an awkward question which is yet to be fully resolved. If the gate is covered by an enemy ZoC, the Eldar must take an engage activation to exit the gate to assault the enemy formation. where the enemy unit is physically on top of the Wraithgate there are different views on what happens. IIRC correctly, the view expressed by the original ERC was that the enemy unit could be engaged by two Eldar units from within the Webway. Other views are that the gate is completely blocked and cannot be used until the offending unit is dislodged; or that there are no restrictions other than the requirement to engage the enemy.
This is definitely a '5 min warm-up question.
2) Supporting FF Hits are allocated after the assault hits have been resolved, but before the assault resolution. Note that this can cause the supporting fire to have no eligible targets remaining, but in the event that their side loses the supporting formation still gets a BM for being
in position to support even if it actually does not fire.
Supporting hits are allocated to those units nearest the supporting formation, Front-to-back as usual. Remember that  supporting units must have LoS and range (15cm) to enemy units that were actually participating in the assault. Supporting fire may not be used against other enemy units from the formation. (This prevents the abuse of supporting fire)