Hosting a repo is the easy part to figure out.

Keeping repositories synced between versions of Debian and architectures is slightly harder but doable.

Best practices for handling uploads from individual developers, making sure all dependencies are included at the same time when a package is published is hard.

Running something like the official Debian unstable -> testing transition of packages (with QA/testing in that loop), and figuring out what rebuilds are necessary is very hard.

So, you didn't actually answer my question directly, but it sounds like you're talking about your own packages?

Yes