[corndoge]

For 1), how?

I'm specifically interested in how you handle packages that use C extensions that link system libraries.

[Tractor8626]

In such cases I use either docker or mmdebstrap.

[corndoge]

Nix would work too, and that fact touches on one of the main advantages of Nix - it solves the problem at a low enough level that it works in all cases.

[Tractor8626]

There is hidden assumption what using one tool for everything makes things easier.

Does it though? If using one tool is harder than using several - there is no advantage here.