Most of those answers should be in the [url=http://www.roleplayerguild.com/topics/3818/posts/ooc?page=1#post-49658]OOC[/url] thread under the information section~ 

To give some quick answers though, Luce is a huge vertically orientated city with the lower reaches being the sort of seedy area where criminals usually hang out, the upper city being a rich and lavish area.

The people know about magic but keyblades are quite unknown. There probably have been keyblade wielders in the past but due to the relative safety of the world before the fracturing keyblades are virtually unknown.

The Blind is sort of a mass tunnel system sort of like a sewer which contains darkness that gets let off by the light they use as an energy source. 

You can make a keyblade wielder yes. Don't have any specific limit on them, just dont want EVERYONE to be one. 

And again like Impy said there, the OOC has a lot more info about teh world and such