FX vs DX

1. Nikon has a Full frame d800 coming out , or its out. I own a d5100 and thinking about moving up to a FX. I saw a you tube video about B&W photography and it premiss was that a Full framed sensor will capture more of the "Dynamic range" then a DX sensor. Any Thoughts
2. 36mega pixels (D800) vs 12mega pixels(D3) I was told that the amount of light will be better captured with a lesser FX mega pixels camera because the pixels are bigger.
3. When you have a DX camera using a DX lens is a 12-24mm lens still a true 12-24mm lens? or do you have to x1.5 still

I know its allot but I'm sure someone knows