Able to access user -OAath2 app without add collaborator

Hi ,

We have created oauth2 app and we planned to access the box api for our client application. 

1. We have used redirect URL is https://developer.box.com/auth/callback is there fine for our production environment also?

2. App level we have add collaborator .As per your current functionality  only 15 members can add as collaborator . without add a collaborator in app level ,can able to access app and box api using client id and redirect url?

3. we need more than 15 members can access the app and api. Any other way to achieve this in single app? 

Thanks in advance. More appreciate will get answer .