Game Center Workflow

Hi, I’m implementing Game Center for an upcoming game; the code is working, and all is peachy. Although, I’ve been using Corona’s example leaderboard and achievments for quick testing. How do I make transition to adding my own leaderboard and acheivments?

In the Game Center Integration tutorial, it instructs to manage an app already uploaded to iTunes Connect. Our game in still in pre-release stages, should I go agead with an upload or wait until the game is ready to release

Cheers.