>>> Very interesting idea you got there, its a huge task.
I would like to give some piece of advice to you since there some issues when you try to gather talent from different people.

First the style, it seems you already thought about this and you gave some reference pics for the people out there. So I think is ok.

Second is the quality, all the drawings you gather must have a very similar quality. And of course not all the artists who send the images will create something in the same level.
You have to be careful about this.

Third and most important is the fan made vs official artwork.
In this final picture you want to make in your list of "done characters" most of those images you want to use (if not all), are official artwork from square, the problem is that mixing official art with fan made stuff will create something too weird and unappealing in the end.
So its better if you stick only to fan-made drawings and discard any official image from square, no matter how appealing and pretty they are.

Well this is something I was thinking about, your idea is great but it have to be carefully planned if you want to make it succeed..