I agree with Crown. I think a "big" channel is based on it's view count, not it's subscribers. The only thing I would add is if you can consistently keep a view count over 20k for about a year, you've hit it big. I say this because there have been channels in the past that blow up because of a trend or a certain video, and get tons of views a day, but typically after a couple months or so, the channel dies. I don't consider that a big channel.