Creating an automated install

Working with a Raspberry Pi 4 Model B with 8GB RAM. I need to deploy dozens of units, thus I want to automate the process, skipping the GUI installer altogether, bootstrapping it just enough so that I can hit it with Ansible. This is the documentation I've been working from:

I'm using this image: ubuntu-mate-20.04.1-beta2-desktop-arm64+raspi.img.xz

I've created /system-boot/user-data:

  version: 1
    hostname: rpi-test-unit
    password: "..."
    username: kiosk
    install-server: yes
      - ssh-rsa ...
    allow-pw: no
    - python3
  package_update: true
  package_upgrade: true

When I boot from my sd card, it hangs at the initial boot screen, i.e. "Ubuntu 20.04" with terminal output about the firmware. Can someone point me to another set of docs to follow, or a tip on what I'm missing?

Thank you!