Was Zed evil before being banished, or would there have been a way to make him realize his powers are no good? Was Zed evil only because of being alone and warped by darkness, or because he was enveloped in darkness from after the box's opening?

I can answer this.
His old master actually was plotting behind the scenes and killed Zed. He himself was a master of the shadows but knew his legitimacy would be ruined if he turned face as the master of the temple. So he intentionally led Zed into finding the box and knew his personality and jealousy of Shen (who the old master honestly hated, what an annoying *****) would lead him into the forbidden ways. He also knew that he would eventually come back and challenge him. So when Zed came back, he killed him and transformed his body because he's a master of shadows, he can do that sort of thing. Problem was, Zed was a bit more powerful than he had thought so the blow that he initially thought would kill him soundlessly and quickly gave Zed a bit of time to cry out in pain.
Twist: his master is actually LeBlanc, working from within to undermine the Ionians by corrupting their most sacred institutions.

Do the Kinkou consider Zed beyond redemption and a personal enemy to balance that they find repugnant, or do they look at him as a small part of a greater issue that must be taken apart slowly, rather than at once?

Here's a question:

What does Zed think of Diana? Both of them have had hardships with getting others to accept a newfound revelation.

Edit: Of course, their stories aren't entirely similar. Diana's worship of the moon was never shown as inherently evil, while Zed's shadow powers were always forbidden knowledge.

How does Zed feel about Varus? How does Varus feel about Zed? When is Skribbles gonna give me that pic of Varus' Tatt?

When is he going to be released?

Somebody (not necessarily Runaan) please explain why Zed cried out in pain but the other dude died.
I am not so steeped in lore that I Understand what is going on here.

What does the Order of Shadow stand for? If balance is a lie to them, what is their truth? I know the Kinkou stand for balance and equilibrium, but don't shadows represent a type of balance as well in a way (i.e. shadows as a distorted reflection of the self, representing our darker/repressed side)?

Are Zed et al. really diametrically opposed to Shen and his colleagues? Do they have a greater agenda that gives their training a purpose?

Does the box relate to anything we know about already in game?

Does Zed have any lieutenants worthy enough to join the Fields of Justice on their own?

It's a Shaco box.

I have to ask since it isn't spelled out, was the Kinkou Order the ninja order destroyed in Zed's lore or were they different organizations? Now that Zed is in possession of the dark arts box, did he enter the league after learning all its contents or is he still training? Were the contents of the box once part of the order's teachings or were they secrets taken from enemies?