These are my configurations for nixos. You are free to use it, however it may be best for you to fork and make your own.
In my experience, you need a larger disk size for the nix store on the installer than is created. As such, I use a swap file/drive, recommended separate drive from the one being installed to.
mkdir /mnt/usb
mount /dev/sdb1 /mnt/usb
fallocate -l 30G /mnt/usb/swap
chmod 600 /mnt/usb/swap
mkswap /mnt/usb/swap
swapon /mnt/usn/swap
mount -o remount,size=20G,noatime /nix/.rw-store
After setting up the extra swap space, clone and enter the nixos repo.
nix-shell -p git
git clone --recursive https://github.com/GRMrGecko/nixos.git
cd nixos/
After you get into the repo, configure the machine to your liking.
./configure.sh
After configuring, install. You can define a tmpdir as the USB drive with TMPDIR=/mnt/usb
if you want to reduce load on RAM.
./install.sh --disk main /dev/sda
After install is complete, you can then rsync the nixos dir to the user account on the install:
nix-shell -p rsync
mount -o compress=zstd /dev/mapper/crypted /mnt/hdd
rsync -av /root/nixos/ /mnt/hdd/home/grmrgecko/nixos/
umount /mnt/hdd