Whatever choices this project makes (I have some opinions, but I think they're not too important) I don't see it mentioning one of the most absolutely critical choices Nix made that was absolutely key to its insane success (at least, IMO, as a hardcore contributor and user for like 10+ years): the monorepo, containing all of the packages and all the libraries for use by everyone downstream, and all contributions trying to go there.
Please do not give into the temptation to just write a version manager and stitch together some hodgepodge and throw the hard problem over the fence to the "community", a set of balkanized repositories to make everything work. It is really really really hard to overstate how much value Nixpkgs gets from going the monorepo route and how much the project has been able to improve, adapt, and overcome things thanks to it. It feels like Nixpkgs regularly pulls off major code-wide changes on an average Tuesday that other projects would balk at.
(It's actually a benefit early on to just keep everything in one repo too, because you can just... clean up all the code in one spot if you do something like make a major breaking change. Huge huge benefit!)
Finally: as a die hard Nix user, I also have been using Buck2 as a kind of thing-that-is-hermetic-cloud-based-and-supports-Windows tool, and it competes in the same space as Zb; a monorepo containing all BUILD files is incredibly important for things to work reliably and it's what I'm exploring right now and seeing if that can be viable. I'm even exploring the possibility of starting from stage0-posix as well. Good luck! There's still work to be done in this space and Nix isn't the final answer, even if I love it.
Please do not give into the temptation to just write a version manager and stitch together some hodgepodge and throw the hard problem over the fence to the "community", a set of balkanized repositories to make everything work. It is really really really hard to overstate how much value Nixpkgs gets from going the monorepo route and how much the project has been able to improve, adapt, and overcome things thanks to it. It feels like Nixpkgs regularly pulls off major code-wide changes on an average Tuesday that other projects would balk at.
(It's actually a benefit early on to just keep everything in one repo too, because you can just... clean up all the code in one spot if you do something like make a major breaking change. Huge huge benefit!)
Finally: as a die hard Nix user, I also have been using Buck2 as a kind of thing-that-is-hermetic-cloud-based-and-supports-Windows tool, and it competes in the same space as Zb; a monorepo containing all BUILD files is incredibly important for things to work reliably and it's what I'm exploring right now and seeing if that can be viable. I'm even exploring the possibility of starting from stage0-posix as well. Good luck! There's still work to be done in this space and Nix isn't the final answer, even if I love it.