Regarding "Beginning of the Revenge" and assassination option: I question if this is really a viable option as described. Based on my playing to option a number of times, with the units as stated (one shadow + ghosts) there is a lot of luck involved and it succeeds much less than half the time.
First, your ghosts really aren't going to do that much damage - 3 attacks @ 40% =~ 1 hit each at 4 or 5 damage, times 5 ghosts =~ 20, which is significant, but without the shadow, it's not likely to kill the leader before he kills them.
So if your shadow doesn't hit in the first turn (which is 25% likely), all you've done is get the orc leader angry. I never managed to win if that happens, the orc leader is just too likely to kill too many of your forces and leave you too weak to kill him.
To kill the orc leader on the first turn, you need your shadow to hit three times. That's going to happen ~5% (.4^3) of the time - I've never had it happen to me.
So your shadow needs to survive the orc leader's counter attack (which will kill it 1/8 of the time) and then survive the orcs attack to attack again on turn 9. Whatever unit the leader decided to attack (seems to always be whichever is most wounded) is very likely to die. If that turns out to be your shadow, you're then hosed, because at that point you're going to be hard pressed to kill the leader with just your ghosts.
Note this leaves you in a real pickle of a decision. If you have your ghosts do ranged attacks, they won't be damaged and the orc leader will almost always attack your shadow because it is more than likely wounded from its melee attack. If you have ghosts do melee attacks, they are rather likely (3/8 I think) to get killed by the counter attack since two hits kills a ghost, so you'll lose some ghosts right there, but if wounded ghosts exist they are likely to draw the attack from the orc leader during his turn, sparing your shadow. Tricky business.
Plus I found about half the time, the orc leader recruits a new unit on turn 7 or 8 which is then in the mix, making things even tougher.
So, a lot of things have to go right for assassination to work - and they have to go right not just once but twice (both orc leaders). I tried it a number of times, and found I could get it to work less than half the time. I think unless you're willing to reload a lot, assassination isn't really a viable option.