I'm very sorry, I did misunderstand! So then do I understand correctly that your concern is primarily with storing and then sharing out pictures and/or videos that take up significant storage space? You want to download and remove them from Central and store them somewhere from where you can publish references to them? You mention 500 submissions a day -- roughly how big are those submissions?
There are two ongoing initiatives you should be aware of. First, it's not currently possible to delete and purge individual submissions, only entire forms. In the next Central release, it will be possible to delete and purge individual submissions. Second, in the next Central version it will also be possible to store files uploaded to Central in S3-compatible storage (External storage for blobs in ODK Central). This won't immediately address the need to make those media files publicly available but it may relieve some of the long-term storage concerns.
Do you already have visualizations in Google Drive that would show data and media like you want it if the data were in Google Drive? You mention @mathieubossaert's experimentation with AppSmith but that doesn't answer the question of where to store the data -- in his case he replicates it into a normalized postgres database. There are also similar things that people have done with CKAN (some description of how), Superset and Google Looker Studio.