I did something similar a few weeks ago and found that https://rclone.org/ worked for me to automatically port Google Photos data to a Nextcloud instance with WebDAV. That being said, it cannot pull the original quality images, only the compressed version.
But are there any reports of people who use this getting locked out of their account? That would make me very leery as well. Otherwise, I wouldn't personally be worried, especially as the goal is to get off Google in the first place.
