1. It takes anywhere from a couple days to as many as 11 days to have an article get through a review. If it requires revision, it usually will be re-examined within a day or two. You may wish to carefully review your articles before submitting them to help keep the time to a minimum and avoid rejections.
2. If you have a heap of existing articles, you might wish to check out the information on usage rights if you haven't already.
3. You can choose monthly or bi-monthly pay, I believe.