The problem is that "once the package is qualified to be included in Debian" is _mostly_ about "has the package metadata been filled in correctly" and the fact

The problem is that "once the package is qualified to be included in Debian" is _mostly_ about "has the package metadata been filled in correctly" and the fact that all your build dependencies also need to be in Debian already. If you want a "simple custom repository" you likely want to go in a different direction and explicitly do things that wouldn't be allowed in the official Debian repositories. For example, dynamic linking is easy when you only support a single Debian release, or when the Debian build/pkg infrastructure handles this for you, but if you run a custom repository you either need a package for each Debian release you care about and have an understanding of things like `~deb13u1` to make sure your upgrade paths work correctly, or use static binaries (which is what I do for my custom repository).