King Taloren

It is for each unsaved wound suffered. When you take damage you suffer each wound one at a time until the model/unit dies so he can only potentially deal 7 wounds and then he dies. And the rest of the unsaved wounds are wasted as overkill and don’t do anything for either player.
Most people just tend to quick resolve things by doing all the damage simultaneously so it occasionally this misconception tends to spring up.

It does not block line of sight. Go reread it.
OBSTACLES
Some terrain features are obstacles that block attacks to targets that lie beyond them. When this is the case, it will be noted on the warscroll for the terrain feature.
When a missile weapon targets an enemy unit that is within 1” of an obstacle then then target receives the benefit of cover if the attacking unit is closer to the obstacle than the defending unit.

Page 10 in the core rules Designer commentary:
Can allied heroes be given an artifact of power? No

You use it once for each unit in range of any unit with the Virulent Discharge ability. So even if you have two units with Virulent Discharge  in range of an enemy unit you only get one roll.

It’s a save after save like deathless spirits.  And you can take it and have three saves.
After the Etheral save you can choose to roll either one first and then use the other afterwards.
But the Sepulchral Plate is only good against regular wounds it will offer no protection against mortal wounds. 
On those regular wounds it essentially gives you a reroll on all failed saves. So you are basically giving yourself 6-10% more saves on the roll.

Yes. You are not required to pile in and attack the unit that you charged. You can pile into any unit as long as it’s the closest enemy  model that it can reach, even if it is 4” or 5” away you can stick other units into combat even if you cannot get in range to attack.

Not entirely because it is -1 to enemy MODELS not unit within 3” of the Dreadscythe unit so unless you can position three units near every single model at best you could inflict -2 on a pair of them. Maybe a -3 on a few with clever positioning. And then be prepared for salt from your opponent for mixing your units all into one big bunch and claiming they are 3 separate units. 
Btw what is the base size on dreads? Cause that is also a factor in trying to get three units bunched together.

This is one of those where, for the Evocators, it’s going to be a question of what everyone agrees on in your area.
In my group we allow climbing up the empty gap without going to the back wall. As if they have ladders or ropes to make it up there. Thus it’s a 5” move and a 7” charge to get into b2b though that only gets one Evocator in range to attack depending on how you place them with the rest either hanging in midair on using the 6” leeway vertical unit coherence.
On the flip side if roles were reversed, flying units ignore vertical movements so it is just a straight line flat on the table. So it would just be however many inches it take to make the charge as if they were on the ground.

Endless spells do not have any allegiance ties outside the fact that only wizards with the allegiance keywords can cast them and do not cost ally points because they are not tied to the allegiance itself.
I.e. you can take Sigmar’s Comet in any army you wish but only a Stormcast Wizard can actually cast the spell. So taking it in any army that cannot ally a Stormcast wizard is useless. 
As long as there unit casting the spell has the proper keyword required they can cast the spell regardless of their current allegiance. So yes a Nurgle army can take Skaven endless spells as long as there is a Skaven wizard included. Even if he also has the Nurgle tag he is still Skaven.

That is completely legal. There is nothing to stop warscroll prayers from being used by every unit that can use them. So far. 

You can use Putrid offering once per each cast you make. It cannot be stacked.
And you can use Grandfather’s Joy as many times as you have command points and separate units to give the blessing. If there is only one unit in range then only once.

Yes. Balewind does not affect the look out sir rules.