I wanted to do something similar with a few HC4's (also to run Kubernetes, incidentally ). I settled on this:
- Install authorized_keys in the image using customize-image.sh - https://docs.armbian.com/Developer-Guide_User-Configurations/#user-provided-image-customization-script
- SSH to each sbc after first boot, enter a root password and then cancel the rest of the setup script. It looked to me like the script does some important things before that point.
- Configure the rest with Ansible.
If you found a better way to boot non-interactively I'd be happy to hear!