I recognize the standard process for installing NixOS is to do a manual custom install including partitioning or to use an installer iso then update the /etc/nixos/configuration.nix file manually.
I have spent a couple days searching for how to make a custom installer iso that provides a customized configuration on install that can simplify the process of setting up multiple device. My goal with this is to have the customizability of the partiotioning based on the device via the GUI then an automated way to install various dependencies and basically have my desired environment on first boot. This could include setting up SSH keys and cloning private repos. (Yes security is obviously a risk with this and this ISO should be destroyed to excessive levels when not in use )
All of that said, I do recognize it would be possible to customize the calamares installer to achieve this but I am crossing my fingers in the hopes that someone else has already done this and I can cheat off their work a bit . If not I will venture down this path and maybe make a extendable process.