First, you get a $25 credit for uploading 250. After 1000, it's .10 per. The payout is $75, so you aren't going to get a payout until you get some sales.
On sales, I had one yesterday. In researching this, I find there are 627 images with one sale each. There are 10 images with more than 1 sale, but this includes 2 that were obviously used for testing, so the most sales for 1 image is 4.