Hey. Not a Discourse pro by any means but you should be able to download backups present on the server to your PC and then delete the backup from the server. You should be able to import the backup from your PC when you wish to use it.
As for your question regarding the GIF’s, if you use an extension like Tenor, I don’t think it occupies any space as the image is rendered from their servers. However, if your users upload GIF’s, that might be a different story.