No, unfortunately there is no automatic duplicate detection in Starter Edition (or Photoshop Elements, for that matter).
Adding photos to categories does NOT remove them from your entire collection. Categories are simply virtual groupings of photos. When you add a photo to a Category, it does NOT disappear from the main photo grid. Your Grid represents all the photos that you've added to the catalog already. If you deleted all your categories, not a single photo would be deleted; just the virtual collection would go away.
As for the grainy appearance of some photos, those either sound like they are low resolution photos to begin with, or they have been disconnected from the original file. If you move a file around using Windows, then it gets disconnected from Starter Edition, and then it can't find the original file to load and show you higher resolution images. You either have to use the Reconnect Missing Files command, and let it run, or manually point it to the files wherever they are, or you just need to delete the references to them in Starter Edition. Deleting the references in Starter Edition does not delete any files from your hard drive, unless you explicitly tell the program to delete the file (which it would do by moving it to the trash, so if you don't empty your trash, you actually don't delete any files using Starter Edition.
Hope that helps. There are no shortcuts that I can think of to make the process of de-duplicating your collection less painful than it sounds. Sorry!
Thank you, maybe if I can get them all on one page, I can work on this. Is
there a way to tell which of the duplicates might be the original?
Also, how do I shut off this Adobe Updater that keeps wanting me to download
an update. I have closed it a dozen times in the last hour, even with Task
Manager ending the process.