This guild raid is not fun at all. I mean, it's only designed for whales. Small guilds with low level player probably don't even give a damn on this. Imagine, a VEEEERRRYYY high wall after just killing a weak treant, lol.
Suggestion:
Unlimited milestones - people have this evil thing called pride and they will do anything to protect it. Yep, the more you contribute the more rewards you reap. This way, everything is fair no people will go insane.
The basics - Normal, Heroic and Legendary (might as well as add the Master) difficulties. As mentioned above, VEEERRRRRYYY high wall. That is just so sudden so why not take it slow first?
DON'T EVER - selling guild raid keys? How about a big NO.
I guess that's all.