yes to all.

https://github.com/nix-community/nixos-generators

And for cloud/dedicated servers perhaps https://github.com/nix-community/nixos-anywhere

(There's also a terraform module ) And for state changes https://github.com/serokell/deploy-rs Or Colmena /nixops/ and x other

For secret handling perhaps https://github.com/ryantm/agenix/ + https://github.com/oddlama/agenix-rekey

The ecosystem is in my experience very well fleshed out (7 yrs of use), as long as you don't require a knowledgebase/wiki/ up2date documentation, it's not been a issue for me since I could always fall back on Linux knowledge and just looking for how other distributions do x / how the thing itself is configured , and looking at how perhaps a existing nix module wraps that

Oh I am converted! Will try to setup system using nix instead of packer.

Yes but with an asterisk. Nixos generators linked elsewhere is a really great tool to take a given nix configuration and build it for consumption in many contexts (eg i use the same one to both build initial proxmox vm images and then also update those running images). The problem is that you will need a hardware-configuration.nix that caters to the end environment. Ive worked around this by pre-generating it and then copying it into the result but I wish there was a better, less manual, process.

Yep for sure! We even have a neat upload-ami cli tool:

https://github.com/NixOS/amis

That's awesome! I think all the missing pieces are in place. :)