Definitely not all at once! When you post a new page, it puts you in the "Fresh" section of the website. You can only show up there once a day, and new updates on the same day don't bump you higher on the Fresh section. You don't wanna blow your visibility all in one go.
2-3 times a week is a pretty good pace if you've got such a huge backlog. Frequent enough to stay visible on the site, but not so often that you're overwhelming your readers. And since you have so many pages, you can opt to update in 2-3 page chunks per episode.