I’ve been explicitly told not to use any open source for a project. I don’t even know what language I’d write it in. We ended up not even quoting for it in the end.

Yeah this only makes sense if the builds start diverging from the open source code, extra features that are closed source.

Hertzner storage box. I think it’s €13/month for 5tb. Just storage with ssh interface. I use restic but most backup systems should work with it.