Yes: https://github.com/beacondb/beacondb-unifiednlp

It does (they of course use their Azure Blob storage under the hood). Forgejo however does not (even though it supports it for releases and packages and Golang has this in their standard library).

I’ll keep the idea in mind.

Technically unlimited, but you obviously need to have enough storage to cache the zip files (and RAM to cache the file index). My server is very small, so I needed to set the limit low.