(1) There's no space between TV channels. They all run directly next to one another, like books on a shelf.
That's not how frequency works, no. It's quantized arbitrarily into numbers, it isn't literally a block in space.
(2) The white space devices operate ON channel not between channels. So if there was an empty slot at 50, the device on connect to the internet ON channel 50.
If this is the case then that's an entirely different matter. The article doesn't mention that, but I don't have reason to argue if you've heard otherwise.
(3) The problem is that 50 is not open in the northeast. It's occupied. The entire TV band is full.
The article and materials I've read previously on the matter suggest that opening whitespace is regional, and for instance "channel 50" wouldn't be available for this use in areas where it was already in use for TV or something.