Do I need to wait for an upload to complete before closing Pages/Numbers? After updating a Pages/Numbers document in iOS, I can go back to the app's file browser to get the list of all of my docs in iCloud. At that moment, the document that I had just updated displays a progress bar with the message "Uploading...". If I exit the app, will the upload complete in the background every time? 

I am getting into this bad habit of waiting before closing my app "just in case the upload needs to complete". I believe that waiting is unnecessary, but I don't know yet how reliable iOS is when uploading to iCloud in the background. What has been your experience so far? Is uploading of iWork apps always completed in the background? What about Wi-Fi versus cellular? Any pointers will help. Thanks!
I've just answered on a post about iOS background processes that can explain this for you.

The short answer of your specific question is: As the application is made by Apple I expect them to use the background upload so you can close it.