@girish Glad to serve.
If the goal is an addon, then...
I think the backup piece should be straight-forward? (I have some more info in the packaging thread about this.) Essentially, you want to make sure the SQLite DB is backed up, and then you backup the filesystem. I have questions about what happens if (say) a restore happens (e.g. what if the filesystem path changes?), but those things can be explored.
There is an administrative API that (once you generate a secret/trusted admin API token) lets you do everything administratively via that API (bucket creation, etc.).
As to a web interface, I would not recommend you create one for end-users. (I suspect this is not what you mean.) You have NextCloud, XBackBone, and other apps that can talk to an S3-compatible backend for file browsing. What people might need/want is a way to:
Create/remove buckets (which, on the backend, you'd use your secret admin key)
Create/remove keys and attach them to buckets
Create/remove administrative keys (for superusers who want to script things against the backend)
Bonus: the ability to designate a bucket as a static site, and then you do the DNS work on the backend to point either a subsubdomain at it (e.g. site.s3.example.com) or a whole new domain (e.g. someothersite.com -> site.s3.example.com)
I suspect you could iterate towards this, if you wanted to. Release it with terminal-only management to start, and work towards an admin interface for common bucket creation/removal-type tasks.
There are things that Garage does not do (e.g. lifecycle rules), so this is not a "full" S3 clone (the way Minio aspired to be). In this regard, SeaweedFS might offer more features (and a built-in admin UI)... so, it might be worth doing a spike to explore it as well. At a glance, it is similar, but it also is intended to scale (e.g. it does Raft consensus and Reed-Solomon EC if you want it) in a way that Garage does not. This might also be a reason to not use Seaweed.
I can poke it with a stick if it would be valuable.
