Do I have the right to transfer/back up my archive into the AO3? After all, I didn’t write all these stories!

You may not have written all the stories, but if you’re the moderator of an archive, you’ve accepted responsibility for keeping them online and accessible. We think that transferring an archive into the AO3 is along the same lines as changing web host or ISP, or installing an updated software package for the archive; it’s like a librarian moving a collection.